Reduce some repetitions in tag type mapping code

Reduce some repetitions in tag type mapping code

* Use a streamlined name for each map, `map_LANGUAGE`, where `LANGUAGE`
  is the CTags parser name from tm_parser.h.  This allows some further
  automation.
* Make sure the maps are referenced at the correct index in
  `parser_map`, even if they were not in the same order as in the
  `TMParserType` enumeration by using explicit sub-object initializers.
* As explicit sub-object initialization might lead to a missing
  initializer for a non-last index going unnoticed, add a check for
  uninitialized entries to properly reject them even for regex parsers.