Explicit locations: add UI features for CLI

Explicit locations: add UI features for CLI

This patch exposes explicit locations to the CLI user.  This enables
users to "explicitly" specify attributes of the breakpoint location
to avoid any ambiguity that might otherwise exist with linespecs.

The general syntax of explicit locations is:
-source SOURCE_FILENAME -line {+-}LINE -function FUNCTION_NAME
-label LABEL_NAME

Option names may be abbreviated, e.g., "-s SOURCE_FILENAME -li 3" and users
may use the completer with either options or values.

gdb/ChangeLog:

	* completer.c: Include location.h.
	(enum match_type): New enum.
	(location_completer): Rename to ...
	(linespec_completer): ... this.
	(collect_explicit_location_matches, backup_text_ptr)
	(explicit_location_completer): New functions.
	(location_completer): "New" function; handle linespec
	and explicit location completions.
	(complete_line_internal): Remove all location completer-specific
	handling.
	* linespec.c (linespec_lexer_lex_keyword, is_ada_operator)
	(find_toplevel_char): Export.
	(linespec_parse_line_offset): Export.
	Issue error if STRING is not numerical.
	(gdb_get_linespec_parser_quote_characters): New function.
	* linespec.h (linespec_parse_line_offset): Declare.
	(get_gdb_linespec_parser_quote_characters): Declare.
	(is_ada_operator): Declare.
	(find_toplevel_char): Declare.
	(linespec_lexer_lex_keyword): Declare.
	* location.c (explicit_to_event_location): New function.
	(explicit_location_lex_one): New function.
	(string_to_explicit_location): New function.
	(string_to_event_location): Handle explicit locations.
	* location.h (explicit_to_event_location): Declare.
	(string_to_explicit_location): Declare.

gdb/testsuite/ChangeLog:

	* gdb.linespec/3explicit.c: New file.
	* gdb.linespec/cpexplicit.cc: New file.
	* gdb.linespec/cpexplicit.exp: New file.
	* gdb.linespec/explicit.c: New file.
	* gdb.linespec/explicit.exp: New file.
	* gdb.linespec/explicit2.c: New file.
	* gdb.linespec/ls-errs.exp: Add explicit location tests.
	* lib/gdb.exp (capture_command_output): Regexp-escape `command'
	before using in the matching pattern.
	Clarify that `prefix' is a regular expression.