Introduce -Xpolymorphic-signature compiler flag as more priority than -XXLanguage:+PolymorphicSignature

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.kt

@@ -134,6 +134,12 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
     )
     var inlineClasses: Boolean by FreezableVar(false)
 
+    @Argument(
+        value = "-Xpolymorphic-signature",
+        description = "Enable experimental support for @PolymorphicSignature (MethodHandle/VarHandle)"
+    )
+    var polymorphicSignature: Boolean by FreezableVar(false)
+
     @Argument(
         value = "-Xlegacy-smart-cast-after-try",
         description = "Allow var smart casts despite assignment in try block"
@@ -336,6 +342,10 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
                 put(LanguageFeature.InlineClasses, LanguageFeature.State.ENABLED)
             }
 
+            if (polymorphicSignature) {
+                put(LanguageFeature.PolymorphicSignature, LanguageFeature.State.ENABLED)
+            }
+
             if (legacySmartCastAfterTry) {
                 put(LanguageFeature.SoundSmartCastsAfterTry, LanguageFeature.State.DISABLED)
             }