diagnostics: SARIF output: add "workingDirectory" property (§3.20.19)

diagnostics: SARIF output: add "workingDirectory" property (§3.20.19)

gcc/ChangeLog:
	* diagnostic-format-sarif.cc
	(sarif_builder::make_artifact_location_object): Make public.
	(sarif_invocation::sarif_invocation): Add param "builder".
	Use it to potentially populate the "workingDirectory" property
	with the result of pwd (§3.20.19).
	(sarif_builder::sarif_builder): Pass *this to m_invocation_obj's
	ctor.

gcc/testsuite/ChangeLog:
	* c-c++-common/diagnostic-format-sarif-file-1.c: Verify that we have
	a "workingDirectory" property.

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