diagnostics: avoid using diagnostic_context's m_printer [PR116613]

As work towards supporting multiple diagnostic outputs (where each
output has its own pretty_printer), avoid using diagnostic_context's
m_printer field.  Instead, use the output format's printer.  Currently
this *is* the dc's printer, but eventually it might not be.

No functional change intended.

gcc/ChangeLog:
	PR other/116613
	* diagnostic-format-json.cc (diagnostic_output_format_init_json):
	Pass in the format.  Use the format's printer when disabling
	colorization.  Move the call to set_output_format into here.
	(diagnostic_output_format_init_json_stderr): Update for above
	change.
	(diagnostic_output_format_init_json_file): Likewise.
	* diagnostic-format-sarif.cc
	(diagnostic_output_format_init_sarif): Use the format's printer
	when disabling colorization.
	* diagnostic-path.cc (selftest::test_empty_path): Use the
	text_output's printer.
	(selftest::test_intraprocedural_path): Likewise.
	(selftest::test_interprocedural_path_1): Likewise.
	(selftest::test_interprocedural_path_2): Likewise.
	(selftest::test_recursion): Likewise.
	(selftest::test_control_flow_1): Likewise.
	(selftest::test_control_flow_2): Likewise.
	(selftest::test_control_flow_3): Likewise.
	(selftest::assert_cfg_edge_path_streq): Likewise.
	(selftest::test_control_flow_5): Likewise.
	(selftest::test_control_flow_6): Likewise.

gcc/testsuite/ChangeLog:
	PR other/116613
	* gcc.dg/plugin/diagnostic_group_plugin.c
	(test_output_format::on_begin_group): Use get_printer () rather
	than accessing m_context.m_printer.
	(test_output_format::on_end_group): Likewise.
	* gcc.dg/plugin/diagnostic_plugin_xhtml_format.c
	(xhtml_builder::m_printer): New field.
	(xhtml_builder::xhtml_builder): Add "pp" param and use it to
	initialize m_printer.
	(xhtml_builder::on_report_diagnostic): Drop "context" param.
	(xhtml_builder::make_element_for_diagnostic): Likewise.  Use
	this->m_printer rather than the context's m_printer.  Pass
	m_printer to call to diagnostic_show_locus.
	(xhtml_builder::emit_diagram): Drop "context" param.
	(xhtml_output_format::on_report_diagnostic): Drop context param
	from call to m_builder.
	(xhtml_output_format::on_diagram): Likewise.
	(xhtml_output_format::xhtml_output_format): Pass result of
	get_printer as printer for builder.
	(diagnostic_output_format_init_xhtml): Use the fmt's printer
	rather than the context's.

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