[CS] NFC: Store ContextualTypeInfo in SyntacticElementTarget

Move the contextual type locator onto
ContextualTypeInfo, and consolidate the separate
fields in SyntacticElementTarget into storing a
ContextualTypeInfo. This then lets us plumb down
the locator for the branch contextual type of an
if/switch expression from the initial constraint
generation, rather than introducing it later. This
should be NFC.

include/swift/Sema/Constraint.h

@@ -25,6 +25,7 @@
 #include "swift/AST/TypeLoc.h"
 #include "swift/Basic/Debug.h"
 #include "swift/Sema/ConstraintLocator.h"
+#include "swift/Sema/ContextualTypeInfo.h"
 #include "swift/Sema/OverloadChoice.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/ilist.h"
@@ -50,23 +51,6 @@ class ConstraintLocator;
 class ConstraintSystem;
 enum class TrailingClosureMatching;
 
-/// Describes contextual type information about a particular element
-/// (expression, statement etc.) within a constraint system.
-struct ContextualTypeInfo {
-  TypeLoc typeLoc;
-  ContextualTypePurpose purpose;
-
-  ContextualTypeInfo() : typeLoc(TypeLoc()), purpose(CTP_Unused) {}
-
-  ContextualTypeInfo(Type contextualTy, ContextualTypePurpose purpose)
-      : typeLoc(TypeLoc::withoutLoc(contextualTy)), purpose(purpose) {}
-
-  ContextualTypeInfo(TypeLoc typeLoc, ContextualTypePurpose purpose)
-      : typeLoc(typeLoc), purpose(purpose) {}
-
-  Type getType() const { return typeLoc.getType(); }
-};
-
 /// Describes the kind of constraint placed on one or more types.
 enum class ConstraintKind : char {
   /// The two types must be bound to the same type. This is the only