Add gcc_rich_location::add_fixit_insert_formatted

Add gcc_rich_location::add_fixit_insert_formatted

This patch adds a support function to class gcc_rich_location
to make it easier for fix-it hints to use idiomatic C/C++
indentation, for use by the patch for PR c++/85523.

gcc/ChangeLog:
	PR c++/85523
	* gcc-rich-location.c (blank_line_before_p): New function.
	(use_new_line): New function.
	(gcc_rich_location::add_fixit_insert_formatted): New function.
	* gcc-rich-location.h
	(gcc_rich_location::add_fixit_insert_formatted): New function.

gcc/testsuite/ChangeLog:
	PR c++/85523
	* gcc.dg/plugin/diagnostic-test-show-locus-generate-patch.c
	(test_add_fixit_insert_formatted_single_line): New function.
	(test_add_fixit_insert_formatted_multiline): New function.
	Extend expected output of generated patch to include fix-it hints
	for these.
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c: Include
	"gcc-rich-location.h".  Add test coverage for
	gcc_rich_location::add_fixit_insert_formatted.

From-SVN: r259783