[ConstraintSystem] Get pattern from pattern binding for uninitialized variable targets

Instead of passing pattern directly, let's fetch it from the pattern
binding and remove extra argument from `SolutionApplicationTarget::forUninitializedVar`.

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -1735,9 +1735,9 @@ class SolutionApplicationTarget {
   }
 
   static SolutionApplicationTarget
-  forUninitializedVar(PatternBindingDecl *binding, unsigned index, Pattern *var,
+  forUninitializedVar(PatternBindingDecl *binding, unsigned index,
                       Type patternTy) {
-    return {binding, index, var, patternTy};
+    return {binding, index, binding->getPattern(index), patternTy};
   }
 
   /// Form a target for a synthesized property wrapper initializer.

lib/Sema/CSGen.cpp

@@ -3950,7 +3950,7 @@ bool ConstraintSystem::generateConstraints(
                                init, dc, patternType, patternBinding, index,
                                /*bindPatternVarsOneWay=*/true)
                          : SolutionApplicationTarget::forUninitializedVar(
-                               patternBinding, index, pattern, patternType);
+                               patternBinding, index, patternType);
 
       if (generateConstraints(target, FreeTypeVariableBinding::Disallow)) {
         hadError = true;