Rename UseExperimental->OptIn, Experimental->RequiresOptIn in compiler tests

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

@@ -1,9 +1,9 @@
-// !USE_EXPERIMENTAL: kotlin.Experimental
+// !USE_EXPERIMENTAL: kotlin.RequiresOptIn
 // FILE: api.kt
 
 package api
 
-@Experimental(Experimental.Level.WARNING)
+@RequiresOptIn(RequiresOptIn.Level.WARNING)
 @Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION)
 annotation class ExperimentalAPI
 
@@ -51,7 +51,7 @@ package usage2
 
 import api.*
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 fun useAll() {
     val c: C = C()
     c.function()
@@ -61,7 +61,7 @@ fun useAll() {
     c.extension()
 }
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 class Use {
     fun useAll(c: C) {
         c.function()