analyzer: port translation_unit_callbacks to pub/sub

analyzer: port translation_unit_callbacks to pub/sub

Simplification/consolidation of some callback logic in analyzer in
favor of using the analyzer pub/sub channel.

No functional change intended.

gcc/analyzer/ChangeLog:
	* analyzer-language.cc: Include "context.h" and "channels.h".
	(finish_translation_unit_callbacks): Delete.
	(register_finish_translation_unit_callback): Delete.
	(run_callbacks): Delete.
	(on_finish_translation_unit): Port from run_callbacks to pub/sub.
	* analyzer-language.h (finish_translation_unit_callback): Delete
	typedef.
	(register_finish_translation_unit_callback): Delete decl.
	* common.h (class translation_unit): New forward decl.
	(struct analyzer_events::on_tu_finished): New.
	(analyzer_events::subscriber::on_message): Add vfunc for
	on_tu_finished messages.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/analyzer_cpython_plugin.cc
	(cpython_analyzer_events_subscriber::on_message): New.
	(plugin_init): Port stashing of named types and global vars to
	pub/sub framework.

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