[FIR-TEST] Add new testdata generated after changes in previous commit

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

@@ -0,0 +1,46 @@
+class IncDec() {
+  operator fun inc() : IncDec = this
+  operator fun dec() : IncDec = this
+}
+
+fun testIncDec() {
+  var x = IncDec()
+  x++
+  ++x
+  x--
+  --x
+  x = x++
+  x = x--
+  x = ++x
+  x = --x
+}
+
+class WrongIncDec() {
+  operator fun inc() : Int = 1
+  operator fun dec() : Int = 1
+}
+
+fun testWrongIncDec() {
+  var x = WrongIncDec()
+  x++
+  <!AMBIGUITY!>++<!>x
+  x<!AMBIGUITY!>--<!>
+  <!AMBIGUITY!>--<!>x
+}
+
+class UnitIncDec() {
+  operator fun inc() : Unit {}
+  operator fun dec() : Unit {}
+}
+
+fun testUnitIncDec() {
+  var x = UnitIncDec()
+  x++
+  ++x
+  x--
+  --x
+  x = x++
+  x = x--
+  x = ++x
+  x = --x
+}