Introduce Experimental and UseExperimental annotations

#KT-22759 In Progress

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

@@ -0,0 +1,88 @@
+// !API_VERSION: 1.3
+// FILE: api.kt
+
+package api
+
+@Experimental(Experimental.Level.WARNING, [Experimental.Impact.COMPILATION])
+@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION)
+annotation class ExperimentalAPI
+
+@ExperimentalAPI
+class C {
+    fun function(): String = ""
+    val property: String = ""
+    class Nested
+    inner class Inner
+}
+
+@ExperimentalAPI
+fun C.extension() {}
+
+// FILE: usage-propagate.kt
+
+package usage1
+
+import api.*
+
+@ExperimentalAPI
+fun useAll() {
+    val c: C = C()
+    c.function()
+    c.property
+    C.Nested()
+    c.Inner()
+    c.extension()
+}
+
+@ExperimentalAPI
+class Use {
+    fun useAll(c: C) {
+        c.function()
+        c.property
+        C.Nested()
+        c.Inner()
+        c.extension()
+    }
+}
+
+// FILE: usage-use.kt
+
+package usage2
+
+import api.*
+
+@UseExperimental(ExperimentalAPI::class)
+fun useAll() {
+    val c: C = C()
+    c.function()
+    c.property
+    C.Nested()
+    c.Inner()
+    c.extension()
+}
+
+@UseExperimental(ExperimentalAPI::class)
+class Use {
+    fun useAll(c: <!EXPERIMENTAL_API_USAGE!>C<!>) {
+        c.function()
+        c.property
+        C.Nested()
+        c.Inner()
+        c.extension()
+    }
+}
+
+// FILE: usage-none.kt
+
+package usage3
+
+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<!>()
+    c.<!EXPERIMENTAL_API_USAGE!>Inner<!>()
+    c.<!EXPERIMENTAL_API_USAGE!>extension<!>()
+}