Add comprehensive C++ operator linespec/location/completion tests

Add comprehensive C++ operator linespec/location/completion tests

This exercises the special handling C++ operators require in several
places in the linespec parser, both the linespec and explicit location
completers, symbol lookup, etc.  Particularly, makes sure all that
works without quoting.

Note that despite the apparent smallish size, this adds thousands of
tests to the testsuite, due to combination explosion (linespecs,
explicit locations, tab completion, complete command, completion at
different points in each function, etc.)

Grows the gdb.linespec/ tests like this:

 -# of expected passes           3464
 +# of expected passes           7823

gdb/testsuite/ChangeLog:
2017-11-25  Pedro Alves  <palves@redhat.com>

	* gdb.linespec/cpls-ops.cc: New file.
	* gdb.linespec/cpls-ops.exp: New file.
	* lib/completion-support.exp (test_complete_prefix_range_re): New,
	factored out from ...
	(test_complete_prefix_range): ... this.