[Parse] Move SyntaxParsingContext to Parse (#14360)

This is only for the Parser.
Also, this resolves layering violation where libAST and libSyntax
depends on each other.

include/swift/AST/Module.h

@@ -81,8 +81,6 @@ namespace swift {
   
 namespace syntax {
   class SourceFileSyntax;
-  class SyntaxParsingContext;
-  class SyntaxParsingContextRoot;
 }
 
 /// Discriminator for file-units.