Introduce Experimental and UseExperimental annotations

#KT-22759 In Progress

compiler/testData/diagnostics/testsWithStdLib/experimental/classMembersOverlyExperimental.kt

@@ -0,0 +1,36 @@
+// !API_VERSION: 1.3
+// FILE: api.kt
+
+package api
+
+@Experimental(Experimental.Level.WARNING, [Experimental.Impact.COMPILATION])
+@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY)
+annotation class ExperimentalAPI
+
+@ExperimentalAPI
+class C {
+    @ExperimentalAPI
+    fun function() {}
+
+    @ExperimentalAPI
+    val property: String = ""
+
+    @ExperimentalAPI
+    class Nested {
+        @ExperimentalAPI
+        fun nestedFunction() {}
+    }
+}
+
+// FILE: usage.kt
+
+package usage
+
+import api.*
+
+fun use() {
+    val c: <!EXPERIMENTAL_API_USAGE!>C<!> = <!EXPERIMENTAL_API_USAGE!>C<!>()
+    c.<!EXPERIMENTAL_API_USAGE!>function<!>()
+    c.<!EXPERIMENTAL_API_USAGE!>property<!>
+    <!EXPERIMENTAL_API_USAGE!>C<!>.<!EXPERIMENTAL_API_USAGE!>Nested<!>().<!EXPERIMENTAL_API_USAGE!>nestedFunction<!>()
+}