Publish 'kotlinx-serialization-compiler-plugin' separately

- Also publish 'kotlinx-serialization-compiler-plugin-embeddable' to be
used with 'kotlin-compiler-embeddable'.
- Now Serialization Maven and Gradle plugins do not embed plugin into
itself, but declare on published one normal dependency.
- 'kotlin-serialization-unshaded' publication is deprecated.

^KT-52811 In Progress

plugins/kotlinx-serialization/build.gradle.kts

@@ -72,6 +72,8 @@ sourceSets {
 
 optInToExperimentalCompilerApi()
 
+publish()
+
 runtimeJar()
 sourcesJar()
 javadocJar()

plugins/kotlinx-serialization/kotlinx-serialization.embeddable/build.gradle.kts

@@ -0,0 +1,19 @@
+plugins {
+    id("org.jetbrains.kotlin.jvm")
+}
+
+dependencies {
+    embedded(project(":kotlinx-serialization-compiler-plugin")) { isTransitive = false }
+}
+
+publish {
+    artifactId = artifactId.replace(".", "-")
+}
+
+runtimeJar(rewriteDefaultJarDepsToShadedCompiler())
+sourcesJarWithSourcesFromEmbedded(
+    project(":kotlinx-serialization-compiler-plugin").tasks.named<Jar>("sourcesJar")
+)
+javadocJarWithJavadocFromEmbedded(
+    project(":kotlinx-serialization-compiler-plugin").tasks.named<Jar>("javadocJar")
+)