Add API Reference

<panel>
    <title><TOC title></title>
    <p><library description></p>
    <img src="github.svg" width="18" alt="GitHub"/> <a href="<GitHub repo URL>">View on GitHub</a><br/><br/>
    <a href="https://kotlinlang.org/api/<api id>/" as="button" icon="arrow-right" icon-position="right">Browse API</a>
</panel>

test.skip('Click on "<TOC title short>" button should open the related page', async ({ page }) => {
    const button = await hoverOverApiElement(page, '<TOC title short>');
    await expect(button).toBeVisible();
    await button.click();
    expect(page.url()).toContain('/api/<api id>/');
});

# .teamcity/BuildParams.kt  (after the KOTLINX_IO_* block)
+  const val KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_TAG = "v0.5.0"
+  const val KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_LABEL = "0.5.0"
+  const val KOTLINX_COLLECTIONS_IMMUTABLE_ID = "kotlinx.collections.immutable"
+  const val KOTLINX_COLLECTIONS_IMMUTABLE_TITLE = KOTLINX_COLLECTIONS_IMMUTABLE_ID

# .teamcity/BuildParams.kt  (in API_URLS)
     "api/$KOTLINX_IO_ID",
     "api/$KOTLINX_METADATA_ID",
+    "api/$KOTLINX_COLLECTIONS_IMMUTABLE_ID",
     "api/${KGP_REFERENCE.urlPart}",

// .teamcity/references/vcsRoots/KotlinxCollectionsImmutable.kt  (new)
package references.vcsRoots

import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_TAG
import common.extensions.VCS
import jetbrains.buildServer.configs.kotlin.vcs.GitVcsRoot

object KotlinxCollectionsImmutable : GitVcsRoot({
  name = "kotlinx.collections.immutable vcs root"
  url = "git@github.com:Kotlin/kotlinx.collections.immutable.git"
  // Pinned to the stable release tag (full ref so the short name isn't resolved as a head).
  branch = VCS.tag(KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_TAG)
  branchSpec = "+:refs/tags/*"
  useTagsAsBranches = true
  authMethod = uploadedKey {
    uploadedKey = "teamcity"
  }
})

// .teamcity/references/builds/kotlinx/collectionsImmutable/KotlinxCollectionsImmutablePrepareDokkaTemplates.kt  (new)
package references.builds.kotlinx.collectionsImmutable

import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_ID
import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_TITLE
import jetbrains.buildServer.configs.kotlin.BuildType
import references.templates.PrepareDokkaTemplate

object KotlinxCollectionsImmutablePrepareDokkaTemplates : BuildType({
    name = "$KOTLINX_COLLECTIONS_IMMUTABLE_ID templates"
    description = "Build dokka templates for Kotlinx Collections Immutable"

    templates(PrepareDokkaTemplate)

    params {
        param("env.ALGOLIA_INDEX_NAME", KOTLINX_COLLECTIONS_IMMUTABLE_ID)
        param("env.API_REFERENCE_NAME", KOTLINX_COLLECTIONS_IMMUTABLE_TITLE)
    }
})

// .teamcity/references/builds/kotlinx/collectionsImmutable/KotlinxCollectionsImmutableBuildApiReference.kt  (new)
package references.builds.kotlinx.collectionsImmutable

import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_ID
import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_LABEL
import references.BuildApiPages
import references.dependsOnDokkaTemplate
import references.scriptBuildHtml
import references.scriptDropSnapshot
import references.vcsRoots.KotlinxCollectionsImmutable

private const val DOKKA_HTML_RESULT = "core/build/dokka/html"

object KotlinxCollectionsImmutableBuildApiReference : BuildApiPages(
    apiId = KOTLINX_COLLECTIONS_IMMUTABLE_ID,
    releaseTag = KOTLINX_COLLECTIONS_IMMUTABLE_RELEASE_LABEL,
    pagesRoot = DOKKA_HTML_RESULT,
    // gradle.properties has `version=0.5.0` + a separate `versionSuffix=SNAPSHOT`; strip the
    // suffix (the default drop-snapshot only rewrites `version=`). Same as datetime.
    stepDropSnapshot = {
        scriptDropSnapshot {
            // language=bash
            scriptContent = """
                #!/bin/bash
                sed -i -E "s/versionSuffix=SNAPSHOT//gi" ./gradle.properties
            """.trimIndent()
        }
    },
    stepBuildHtml = {
        scriptBuildHtml { tasks = ":kotlinx-collections-immutable:dokkaGenerate" }
    },
    init = {
        vcs {
            root(KotlinxCollectionsImmutable)
        }
        dependencies {
            dependsOnDokkaTemplate(KotlinxCollectionsImmutablePrepareDokkaTemplates, "core/dokka-templates")
        }
    })

// .teamcity/references/builds/kotlinx/collectionsImmutable/KotlinxCollectionsImmutableBuildSearchIndex.kt  (new)
package references.builds.kotlinx.collectionsImmutable

import BuildParams.KOTLINX_COLLECTIONS_IMMUTABLE_ID
import templates.TemplateSearchIndex

object KotlinxCollectionsImmutableBuildSearchIndex : TemplateSearchIndex({
    name = "$KOTLINX_COLLECTIONS_IMMUTABLE_ID search"
    description = "Build search index for Kotlinx Collections Immutable"

    params {
        param("env.ALGOLIA_INDEX_NAME", "$KOTLINX_COLLECTIONS_IMMUTABLE_ID")
    }

    dependencies {
        dependency(KotlinxCollectionsImmutableBuildApiReference) {
            snapshot {}
            artifacts {
                artifactRules = """
                    pages.zip!** => dist/api/$KOTLINX_COLLECTIONS_IMMUTABLE_ID/
                """.trimIndent()
                cleanDestination = true
            }
        }
    }
})

# .teamcity/references/BuildApiReferencesProject.kt  (imports)
+import references.builds.kotlinx.collectionsImmutable.KotlinxCollectionsImmutableBuildApiReference
+import references.builds.kotlinx.collectionsImmutable.KotlinxCollectionsImmutableBuildSearchIndex
+import references.builds.kotlinx.collectionsImmutable.KotlinxCollectionsImmutablePrepareDokkaTemplates

# .teamcity/references/BuildApiReferencesProject.kt  (Project body)
+    buildType(KotlinxCollectionsImmutableBuildApiReference)
+    buildType(KotlinxCollectionsImmutableBuildSearchIndex)
+    buildType(KotlinxCollectionsImmutablePrepareDokkaTemplates)
...
+    vcsRoot(KotlinxCollectionsImmutable)

# docs/kr.tree  (inside <toc-element toc-title="API reference">)
     <toc-element toc-title="Date and time (kotlinx-datetime)" href="https://kotlinlang.org/api/kotlinx-datetime/"/>
+    <toc-element toc-title="Immutable collections (kotlinx.collections.immutable)" href="https://kotlinlang.org/api/kotlinx.collections.immutable/"/>
     <toc-element toc-title="JVM Metadata (kotlinx-metadata-jvm)" href="https://kotlinlang.org/api/kotlinx-metadata-jvm/"/>

# docs/topics/api-references.md  (inside <panels columns="2">, after the datetime panel)
         </panel>
+        <panel>
+            <title>Immutable collections (kotlinx.collections.immutable)</title>
+            <p>A multiplatform library providing immutable and persistent collection interfaces and implementations. It offers efficient copy-on-write operations that share structure between versions, so updating a collection doesn't copy the whole thing.</p>
+            <img src="github.svg" width="18" alt="GitHub"/> <a href="https://github.com/Kotlin/kotlinx.collections.immutable">View on GitHub</a><br/><br/>
+            <a href="https://kotlinlang.org/api/kotlinx.collections.immutable/" as="button" icon="arrow-right" icon-position="right">Browse API</a>
+        </panel>
         <panel>
             <title>Kotlin Gradle plugins (kotlin-gradle-plugin)</title>

// test/production/api-navigation.spec.ts  (new test next to the others; skipped until the page is live)
test.skip('Click on "Immutable collections" button should open the related page', async ({ page }) => {
    const immutableButton = await hoverOverApiElement(page, 'Immutable collections');
    await expect(immutableButton).toBeVisible();
    await immutableButton.click();
    expect(page.url()).toContain('/api/kotlinx.collections.immutable/');
});