The previous implementation of summarized dumps within
region_model::dump_to_pp showed only the "top-level" keys within the
current frame and for globals, and thus didn't e.g. show the values
of fields of structs, or elements of arrays.

This patch rewrites it to gather a vec of representative path_vars
for all regions, using this to generate the dump, so that all expressible
lvalues ought to make it to the summarized dump.

gcc/analyzer/ChangeLog:
	* region-model.cc: Include "stor-layout.h".
	(region_model::dump_to_pp): Rather than calling
	dump_summary_of_map on each of the current frame and the globals,
	instead get a vec of representative path_vars for all regions,
	and then dump a summary of all of them.
	(region_model::dump_summary_of_map): Delete, rewriting into...
	(region_model::dump_summary_of_rep_path_vars): ...this new
	function, working on a vec of path_vars.
	(region_model::set_value): New overload.
	(region_model::get_representative_path_var): Rename
	"parent_region" local to "parent_reg" and consolidate with other
	local.  Guard test for grandparent being stack on parent_reg being
	non-NULL.  Move handling for parent being an array_region to
	within guard for parent_reg being non-NULL.
	(selftest::make_test_compound_type): New function.
	(selftest::test_dump_2): New selftest.
	(selftest::test_dump_3): New selftest.
	(selftest::test_stack_frames): Update expected output from
	simplified dump to show "a" and "b" from parent frame and "y" in
	child frame.
	(selftest::analyzer_region_model_cc_tests): Call test_dump_2 and
	test_dump_3.
	* region-model.h (region_model::set_value): New overload decl.
	(region_model::dump_summary_of_map): Delete.
	(region_model::dump_summary_of_rep_path_vars): New.