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

libraries/tools/kotlin-main-kts-test/build.gradle.kts

@@ -15,7 +15,7 @@ dependencies {
     testApi(commonDependency("junit"))
     testApi(projectTests(":kotlin-scripting-compiler")) { isTransitive = false }
     testImplementation(project(":kotlin-compiler-embeddable"))
-    kotlinxSerializationGradlePluginClasspath(project(":kotlin-serialization")) { isTransitive = false }
+    kotlinxSerializationGradlePluginClasspath(project(":kotlinx-serialization-compiler-plugin.embeddable")) { isTransitive = false }
 }
 
 sourceSets {
@@ -24,7 +24,7 @@ sourceSets {
 }
 
 projectTest(parallel = true) {
-    dependsOn(":dist", ":kotlin-serialization:jar")
+    dependsOn(":dist", ":kotlinx-serialization-compiler-plugin.embeddable:embeddable")
     val localKotlinxSerializationPluginClasspath: FileCollection = kotlinxSerializationGradlePluginClasspath
     doFirst {
         systemProperty("kotlin.script.test.kotlinx.serialization.plugin.classpath", localKotlinxSerializationPluginClasspath.asPath)

libraries/tools/kotlin-main-kts-test/test/org/jetbrains/kotlin/mainKts/test/mainKtsTest.kt

@@ -246,8 +246,6 @@ class MainKtsTest {
     @Test
     fun testHelloSerialization() {
         // the embeddable plugin is needed for this test, because embeddable compiler is used.
-        // furtunately appropriate gradle plugin can serve as an embeddable compiler plugin now
-        // so, the path to it is prepared in the build file
         val serializationPluginClasspath = System.getProperty("kotlin.script.test.kotlinx.serialization.plugin.classpath")!!
         val out = captureOut {
             val res = evalFileWithConfigurations(