Utilize TypeReprs for type checking.

-Refactor Parser to stop creating types
-Refactor TypeChecker to create types by resolving TypeReprs.
-Remove "validation" bit from the type system.
  We don't need to "validate" every type that gets created but there's still a validation bit in TypeLoc,
  necessary because of generic substitutions.

Swift SVN r6326

include/swift/AST/Pattern.h

@@ -313,7 +313,6 @@ class TypedPattern : public Pattern {
 public:
   TypedPattern(Pattern *pattern, TypeLoc tl)
     : Pattern(PatternKind::Typed), SubPattern(pattern), PatType(tl) {
-    assert(pattern->isImplicit() == !tl.hasLocation());
     if (pattern->isImplicit())
       setImplicit();
   }