C#: Replace old-style unbind with pragmas.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/Conversion.qll

@@ -232,14 +232,9 @@ private module Identity {
    */
   pragma[nomagic]
   private predicate convTypeArguments(Type fromTypeArgument, Type toTypeArgument, int i) {
-    exists(int j |
-      fromTypeArgument = getTypeArgumentRanked(_, _, i) and
-      toTypeArgument = getTypeArgumentRanked(_, _, j) and
-      i <= j and
-      j <= i
-    |
-      convIdentity(fromTypeArgument, toTypeArgument)
-    )
+    fromTypeArgument = getTypeArgumentRanked(_, _, pragma[only_bind_into](i)) and
+    toTypeArgument = getTypeArgumentRanked(_, _, pragma[only_bind_into](i)) and
+    convIdentity(fromTypeArgument, toTypeArgument)
   }
 
   pragma[nomagic]
@@ -929,19 +924,16 @@ private module Variance {
   private predicate convTypeArguments(
     TypeArgument fromTypeArgument, TypeArgument toTypeArgument, int i, TVariance v
   ) {
-    exists(int j |
-      fromTypeArgument = getTypeArgumentRanked(_, _, i, _) and
-      toTypeArgument = getTypeArgumentRanked(_, _, j, _) and
-      i <= j and
-      j <= i
-    |
+    fromTypeArgument = getTypeArgumentRanked(_, _, pragma[only_bind_into](i), _) and
+    toTypeArgument = getTypeArgumentRanked(_, _, pragma[only_bind_into](i), _) and
+    (
       convIdentity(fromTypeArgument, toTypeArgument) and
       v = TNone()
       or
-      convRefTypeTypeArgumentOut(fromTypeArgument, toTypeArgument, j) and
+      convRefTypeTypeArgumentOut(fromTypeArgument, toTypeArgument, i) and
       v = TOut()
       or
-      convRefTypeTypeArgumentIn(toTypeArgument, fromTypeArgument, j) and
+      convRefTypeTypeArgumentIn(toTypeArgument, fromTypeArgument, i) and
       v = TIn()
     )
   }