[LL FIR] make result$$ property independent

Now we can resolve this generated property in the same way
as other regular properties.
This is the pre-step for independent script initializers

^KT-65344
^KT-65523

analysis/low-level-api-fir/testData/nonLocalDeclarationAnchors/statements.txt

@@ -23,5 +23,5 @@ build {
     version = "321"
 }/* <-- */
 
-builder.execute()
+/* anchor --> */builder.execute()/* <-- */
 /* <-- */

analysis/low-level-api-fir/testData/nonLocalDeclarationAnchors/topLevelFor.txt

@@ -1,4 +1,4 @@
-/* anchor --> */for ((index, _) in emptyList<Int>().withIndex()) {
+/* anchor --> *//* anchor --> */for ((index, _) in emptyList<Int>().withIndex()) {
 
-}
+}/* <-- */
 /* <-- */