FIR: Fix scope intersection types

Otherwise overload resolution ambiguity is reported in the test

compiler/testData/diagnostics/tests/IncDec.fir.kt

@@ -23,9 +23,9 @@ class WrongIncDec() {
 fun testWrongIncDec() {
   var x = WrongIncDec()
   x++
-  <!AMBIGUITY!>++<!>x
+  ++x
   x--
-  <!AMBIGUITY!>--<!>x
+  --x
 }
 
 class UnitIncDec() {
@@ -43,4 +43,4 @@ fun testUnitIncDec() {
   x = x--
   x = ++x
   x = --x
-}
+}