Move completion parsing to parser_state

Move completion parsing to parser_state

This moves the globals and functions related to parsing for completion
to parser_state.  A new structure is introduced in order to return
completion results from the parse back to
parse_expression_for_completion.

gdb/ChangeLog
2019-04-04  Tom Tromey  <tom@tromey.com>

	* rust-exp.y (rust_parser::lex_identifier, rustyylex)
	(rust_parser::convert_ast_to_expression, rust_parse)
	(rust_lex_test_completion, rust_lex_tests): Update.
	* parser-defs.h (struct expr_completion_state): New.
	(struct parser_state) <parser_state>: Add completion parameter.
	<mark_struct_expression, mark_completion_tag>: New methods.
	<parse_completion, m_completion_state>: New members.
	(prefixify_expression, null_post_parser): Update.
	(mark_struct_expression, mark_completion_tag): Don't declare.
	* parse.c (parse_completion, expout_last_struct)
	(expout_tag_completion_type, expout_completion_name): Remove
	globals.
	(parser_state::mark_struct_expression)
	(parser_state::mark_completion_tag): Now methods.
	(prefixify_expression): Add last_struct parameter.
	(prefixify_subexp): Likewise.
	(parse_exp_1): Update.
	(parse_exp_in_context): Add cstate parameter.  Update.
	(parse_expression_for_completion): Create an
	expr_completion_state.
	(null_post_parser): Add "completion" parameter.
	* p-exp.y: Update rules.
	(yylex): Update.
	* language.h (struct language_defn) <la_post_parser>: Add
	"completing" parameter.
	* go-exp.y: Update rules.
	(lex_one_token): Update.
	* expression.h (parse_completion): Don't declare.
	* d-exp.y: Update rules.
	(lex_one_token): Update rules.
	* c-exp.y: Update rules.
	(lex_one_token): Update.
	* ada-lang.c (resolve): Add "parse_completion" parameter.
	(resolve_subexp): Likewise.
	(ada_resolve_function): Likewise.