diagnostics: rename option_manager to option_id_manager and split out from context.h

diagnostics: rename option_manager to option_id_manager and split out from context.h

This patch splits out class option_manager to its own header,
and renames it to class option_id_manager to better describe its
purpose.

No functional change intended.

gcc/ChangeLog:
	* diagnostics/context.cc: Update for renaming of option_manager to
	option_id_manager and of context::m_option_mgr to
	context::m_option_id_mgr.
	* diagnostics/context.h: Likewise, moving class declaration to a
	new diagnostics/option-id-manager.h.
	* diagnostics/lazy-paths.cc: Likewise.
	* diagnostics/option-id-manager.h: New file, from material in
	diagnostics/context.h.
	* lto-wrapper.cc: Update for renaming of option_manager to
	option_id_manager.
	* opts-common.cc: Likewise.
	* opts-diagnostic.h: Likewise.
	* opts.cc: Likewise.
	* toplev.cc: Likewise.

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