diagnostics: move gcc/selftest-diagnostic.{h,cc} -> gcc/diagnostics/selftest-context...

diagnostics: move gcc/selftest-diagnostic.{h,cc} -> gcc/diagnostics/selftest-context.{h,cc}

No functional change intended.

gcc/ChangeLog:
	* Makefile.in (OBJS-libcommon): Replace selftest-diagnostic.o with
	diagnostics/selftest-context.o.
	* diagnostic.cc: Update for move of selftest-diagnostic.h to
	diagnostics/selftest-context.h.
	* diagnostics/html-sink.cc: Likewise.
	* diagnostics/lazy-paths.cc: Likewise.
	* diagnostics/output-spec.cc: Likewise.
	* diagnostics/paths-output.cc: Likewise.
	* diagnostics/sarif-sink.cc: Likewise.
	* selftest-diagnostic.cc: Move to...
	* diagnostics/selftest-context.cc: ...here and update for move of
	header file.
	* selftest-diagnostic.h: Move to...
	* diagnostics/selftest-context.h: ...here.
	* diagnostics/source-printing.cc: Update for move of
	selftest-diagnostic.h to diagnostics/selftest-context.h.

gcc/c-family/ChangeLog:
	* c-format.cc: Update for move of selftest-diagnostic.h to
	diagnostics/selftest-context.h.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/expensive_selftests_plugin.cc: Update for move of
	selftest-diagnostic.h to diagnostics/selftest-context.h.

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