PR14992: Debug Info: Support more non-type template parameters

* Provide DW_TAG_template_value_parameter for pointers, function
  pointers, member pointers, and member function pointers (still missing
  support for template template parameters which GCC encodes as a
  DW_TAG_GNU_template_template_param)
* Provide values for all but the (member & non-member) function pointer case.
  Simple constant integer values for member pointers (offset within the
  object) and address for the value pointer case. GCC doesn't provide a
  value for the member function pointer case so I'm not sure how, if at
  all, GDB supports encoding that. & non-member function pointers should
  follow shortly in a subsequent patch.
* Null pointer value encodings of all of these types, including
  correctly encoding null data member pointers as -1.