Use OPT_IN instead of EXPERIMENTAL in diagnostic names

compiler/fir/analysis-tests/testData/resolveWithStdlib/problems/KtFirCompositeScope.kt

@@ -2,7 +2,7 @@ interface KtScope {
     fun getAllNames(): Set<String>
 }
 
-inline fun <E> buildSet(@<!EXPERIMENTAL_API_USAGE_ERROR!>BuilderInference<!> builderAction: MutableSet<E>.() -> Unit): Set<E> {
+inline fun <E> buildSet(@<!OPT_IN_USAGE_ERROR!>BuilderInference<!> builderAction: MutableSet<E>.() -> Unit): Set<E> {
     return null!!
 }