Add WordComponentParser class
Recreate WordParser class

In this refactoring commit, the former WordParser class is removed and
the WordParserBase class is renamed to WordParser, which is now a non-
abstract class. The implementation of the new WordParser class is more
simpler than the previous WordParserBase class thanks to the
WordComponentParser class that was introduced in the previous commit.
Rename stub classes in WordParserTest

The stubs' functionality is not actually related to raw strings.
Rename WordParser::mCurrentComponentParser to mComponentParser

The word "current" is not very informative...