Flip Gradle plugin kotlin_module names

Now common SourceSet output will have '_common' suffix, while all
variants will have the same name - '<module-name>.kotlin_module'.

This change is required for KSP as short-term workaround, as they
are using some internal properties/methods, which was mangled before
this change and hard to access in different variants.

^KT-52138 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/UpToDateIT.kt

@@ -100,7 +100,7 @@ class UpToDateIT : KGPBaseTest() {
         val originalPaths get() = originalCompilerCp.map { it.replace("\\", "/") }.joinToString(", ") { "'$it'" }
 
         override fun initProject(project: TestProject) = with(project) {
-            val pluginSuffix = "kotlin_gradle_plugin"
+            val pluginSuffix = "kotlin_gradle_plugin_common"
             buildGradle.appendText(
                 "\nafterEvaluate { println 'compiler_cp=' + compileKotlin.getDefaultCompilerClasspath\$$pluginSuffix().toList() }"
             )