diagnostics: improvements to experimental-html output [PR116792]

diagnostics: improvements to experimental-html output [PR116792]

Add barebones support for
* diagnostic metadata rules
* quoted source
* generated patches
* execution paths

gcc/ChangeLog:
	PR other/116792
	* diagnostic-format-html.cc: Include "diagnostic-format-text.h",
	"pretty-print-urlifier.h" and "edit-context.h".
	(html_builder::html_builder): Fix indentation in decl.
	(html_builder::make_element_for_diagnostic): Split out metadata
	code into make_element_for_metadata.  Call
	make_element_for_source, make_element_for_path, and
	make_element_for_patch.
	(html_builder::make_element_for_source): New.
	(html_builder::make_element_for_path): New.
	(html_builder::make_element_for_patch): New.
	(html_builder::make_metadata_element): New.
	(html_builder::make_element_for_metadata): New.
	(html_output_format::get_builder): New.
	(selftest::test_html_diagnostic_context::get_builder): New.
	(selftest::test_simple_log): Update test to print a quoted string,
	and verify that it uses a "gcc-quoted-text" span.
	(selftest::test_metadata): New.
	(selftest::diagnostic_format_html_cc_tests): Call it.

gcc/testsuite/ChangeLog:
	PR other/116792
	* gcc.dg/html-output/missing-semicolon.py: Verify that we don't
	have an empty "gcc-annotated-source" and we do have a
	"gcc-generated-patch".
	* gcc.dg/plugin/diagnostic-test-metadata-html.c: New test.
	* gcc.dg/plugin/diagnostic-test-metadata-html.py: New test script.
	* gcc.dg/plugin/diagnostic-test-paths-2.c: Add
	"-fdiagnostics-add-output=experimental-html" to options. Add
	invocation of diagnostic-test-paths-2.py.
	* gcc.dg/plugin/diagnostic-test-paths-2.py: New test script.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add
	diagnostic-test-metadata-html.c.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>