KT-3182 Prohibit val/var keywords at for-loop counter.

#KT-3182 fixed

compiler/testData/diagnostics/tests/controlStructures/valVarLoopParameter.kt

@@ -0,0 +1,9 @@
+fun f() {
+    for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>val<!> i in 1..4) {
+
+    }
+
+    for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>var<!> i in 1..4) {
+
+    }
+}