FIR: add temporary access to Enum.getDeclaringClass (see KT-49653)

compiler/testData/diagnostics/tests/duplicateJvmSignature/finalMembersFromBuiltIns/enumMembers.fir.kt

@@ -1,6 +1,6 @@
 enum class E {
     ENTRY;
 
-    fun getDeclaringClass() {}
+    fun <!VIRTUAL_MEMBER_HIDDEN!>getDeclaringClass<!>() {}
     fun finalize() {}
 }

compiler/testData/diagnostics/tests/enum/declaringClass.fir.kt

@@ -4,6 +4,6 @@
 import java.util.*
 
 fun <E : Enum<E>> foo(values: Array<E>) {
-    EnumSet.noneOf(values.first().<!UNRESOLVED_REFERENCE!>declaringClass<!>)
-    EnumSet.noneOf(values.first().<!UNRESOLVED_REFERENCE!>getDeclaringClass<!>())
+    EnumSet.noneOf(values.first().declaringClass)
+    EnumSet.noneOf(values.first().getDeclaringClass())
 }

compiler/testData/diagnostics/tests/targetedBuiltIns/backwardCompatibility/finalize.fir.kt

@@ -1,7 +1,7 @@
 enum class TestEnum {
     ENTRY;
 
-    fun getDeclaringClass() {}
+    fun <!VIRTUAL_MEMBER_HIDDEN!>getDeclaringClass<!>() {}
     fun finalize() {}
 }