Use OPT_IN instead of EXPERIMENTAL in diagnostic names

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

@@ -1,4 +1,4 @@
-fun <T> foo(@<!EXPERIMENTAL_API_USAGE_ERROR!>BuilderInference<!> block: MutableList<T>.() -> Unit): T = null!!
+fun <T> foo(@<!OPT_IN_USAGE_ERROR!>BuilderInference<!> block: MutableList<T>.() -> Unit): T = null!!
 
 fun takeString(s: String) {}
 

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

@@ -2,7 +2,7 @@ class DropDownComponent<T : Any>(val initialValues: List<T>)
 
 fun test(strings: List<String>) {
     val dropDown = DropDownComponent(
-        initialValues = <!EXPERIMENTAL_API_USAGE_ERROR!>buildList<!> {
+        initialValues = <!OPT_IN_USAGE_ERROR!>buildList<!> {
             addAll(strings)
         }
     )

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)
 }