[FIR] Rename PLUGIN_ANNOTATION_AMBIGUITY to COMPILER_REQUIRED_ANNOTATION_AMBIGUITY

This diagnostic may be reported even without any compiler plugins (e.g.
  for annotation named `Target` or `Deprecated`), so the old name
  and message were quite confusing

^KT-64654

plugins/fir-plugin-prototype/testData/diagnostics/status/metaAnnotationClashesWithSupertype.kt

@@ -11,7 +11,7 @@ open class Base {
 }
 
 class Derived : Base() {
-    @<!PLUGIN_ANNOTATION_AMBIGUITY!>Open<!> // should be an error
+    @<!COMPILER_REQUIRED_ANNOTATION_AMBIGUITY!>Open<!> // should be an error
     @Ann // should be ok
     class ShouldBeFinal
 }