Use OPT_IN instead of EXPERIMENTAL in diagnostic names

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/builderInferenceFromStdlib.kt

@@ -1,5 +1,5 @@
 fun test_1() {
-    val list = <!EXPERIMENTAL_API_USAGE_ERROR!>buildList<!> {
+    val list = <!OPT_IN_USAGE_ERROR!>buildList<!> {
         add("")
     }
     takeList(list)
@@ -12,7 +12,7 @@ fun test_2() {
     takeList(list)
 }
 
-fun <E> myBuildList(@<!EXPERIMENTAL_API_USAGE_ERROR!>BuilderInference<!> builderAction: MutableList<E>.() -> Unit): List<E> {
+fun <E> myBuildList(@<!OPT_IN_USAGE_ERROR!>BuilderInference<!> builderAction: MutableList<E>.() -> Unit): List<E> {
     return ArrayList<E>().apply(builderAction)
 }