Introduce RequiresOptIn and OptIn annotations

RequiresOptIn should be used now instead of Experimental, OptIn instead
of UseExperimental. See https://github.com/Kotlin/KEEP/pull/201.

This change adds the new declarations only to the stdlib, and supports
them in the compiler. Because of the way compiler loads annotations, we
need to bootstrap it first before deprecating the old annotations and
updating tests.

 #KT-34647 Fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dsl/ExperimentalDceDsl.kt

@@ -6,5 +6,6 @@
 package org.jetbrains.kotlin.gradle.targets.js.dsl
 
 @Experimental(level = Experimental.Level.WARNING)
+// TODO: @RequiresOptIn(level = RequiresOptIn.Level.WARNING)
 @Target(AnnotationTarget.FUNCTION)
-annotation class ExperimentalDceDsl
+annotation class ExperimentalDceDsl

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dsl/ExperimentalDistributionDsl.kt

@@ -6,5 +6,6 @@
 package org.jetbrains.kotlin.gradle.targets.js.dsl
 
 @Experimental(level = Experimental.Level.WARNING)
+// TODO: @RequiresOptIn(level = RequiresOptIn.Level.WARNING)
 @Target(AnnotationTarget.FUNCTION)
-annotation class ExperimentalDistributionDsl
+annotation class ExperimentalDistributionDsl