[Gradle] BuildKotlinToolingMetadataTask: Ensure clean output directory

This is done to prevent unwanted files from also being located
in the output directory. If the task is executed it is expected
that the output directory only contains this one file.

This is necessary, since *everything* located in the output directory
will potentially be bundled into release apks.

^KT-48019

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/tooling/BuildKotlinToolingMetadataTask.kt

@@ -57,7 +57,7 @@ abstract class BuildKotlinToolingMetadataTask : DefaultTask() {
     @get:OutputDirectory
     val outputDirectory: File = project.buildDir.resolve("kotlinToolingMetadata")
 
-    @get:OutputFile
+    @get:Internal /* Covered by 'outputDirectory' */
     val outputFile: File = outputDirectory.resolve("kotlin-tooling-metadata.json")
 
     @get:Internal
@@ -71,7 +71,10 @@ abstract class BuildKotlinToolingMetadataTask : DefaultTask() {
 
     @TaskAction
     internal fun createToolingMetadataFile() {
+        /* Ensure output directory exists and is empty */
         outputDirectory.mkdirs()
+        outputDirectory.listFiles().orEmpty().forEach { file -> file.deleteRecursively() }
+
         outputFile.writeText(kotlinToolingMetadataJson)
     }
 }