[Parse] Remove unnecessary dependencies to Parser.h

C++ swift::Parser is going to be replaced with SwiftParser+ASTGen.
Direct dependencies to it should be removed. Before that, remove
unnecessary '#include "swift/Parse/Parser.h"' to clarify what actually
depends on 'swift::Parser'.

Split 'swift::parseDeclName()' et al. into the dedicated files.

include/swift/Migrator/FixitFilter.h

@@ -18,6 +18,7 @@
 #define SWIFT_MIGRATOR_FIXITFILTER_H
 
 #include "swift/AST/DiagnosticConsumer.h"
+#include "swift/AST/DiagnosticsParse.h"
 #include "swift/AST/DiagnosticsSema.h"
 
 namespace swift {