[Compiler] Mark all entrypoints to compiler API as experimental

compiler/cli/build.gradle.kts

@@ -53,6 +53,10 @@ sourceSets {
     "test" { }
 }
 
+allprojects {
+    optInToExperimentalCompilerApi()
+}
+
 tasks.withType<org.jetbrains.kotlin.gradle.dsl.KotlinCompile<*>> {
     kotlinOptions {
         languageVersion = "1.4"

compiler/cli/cli-common/build.gradle.kts

@@ -21,6 +21,8 @@ sourceSets {
     "test" {}
 }
 
+optInToExperimentalCompilerApi()
+
 tasks.getByName<Jar>("jar") {
     //excludes unused bunch files
     exclude("META-INF/extensions/*.xml.**")