val / var are now forbidden on a loop multi declaration parameter #KT-6274 Fixed

VAL_OR_VAR_ON_LOOP_MULTI_PARAMETER error added
KtValVarKeywordOwner interface added for PSIs that have getValOrVarKeyword method

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

@@ -1,3 +1,18 @@
+class Pair {
+    operator fun component1(): Int = null!!
+    operator fun component2(): Int = null!!
+}
+
+class Coll {
+    operator fun iterator(): It = It()
+}
+
+class It {
+    operator fun next() = Pair()
+    operator fun hasNext() = false
+}
+
+
 fun f() {
     for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>val<!> i in 1..4) {
 
@@ -6,4 +21,12 @@ fun f() {
     for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>var<!> i in 1..4) {
 
     }
+
+    for (<!VAL_OR_VAR_ON_LOOP_MULTI_PARAMETER!>val<!> (i,j) in Coll()) {
+
+    }
+
+    for (<!VAL_OR_VAR_ON_LOOP_MULTI_PARAMETER!>var<!> (i,j) in Coll()) {
+
+    }
 }