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

compiler/testData/diagnostics/testsWithStdLib/experimental/deeplyNestedClass.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
 
@@ -36,12 +36,12 @@ package usage2
 
 import api.*
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 fun use1() {
     C.D.E.F()
 }
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 fun use2(f: C.D.E.F) = f.hashCode()
 
 // FILE: usage-none.kt