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

compiler/testData/diagnostics/testsWithStdLib/experimental/bodyUsages.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)
 annotation class ExperimentalAPI
 
 interface I
@@ -19,12 +19,12 @@ import api.*
 
 open class Base(val i: I)
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 class Derived : Base(Impl())
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 class Delegated : I by Impl()
 
-@UseExperimental(ExperimentalAPI::class)
+@OptIn(ExperimentalAPI::class)
 val delegatedProperty by Impl()
 operator fun I.getValue(x: Any?, y: Any?) = null