diagnostics: SARIF output: use std::unique_ptr throughout

diagnostics: SARIF output: use std::unique_ptr throughout

No functional change intended.

gcc/analyzer/ChangeLog:
	* checker-event.cc (maybe_add_sarif_properties): Update setting
	of "original_fndecl" to use typesafe unique_ptr variant of
	json::object::set.

gcc/ChangeLog:
	* diagnostic-format-sarif.cc: Include "make-unique.h".  Convert
	raw pointers to std::unique_ptr throughout to indicate ownership,
	adding comments in the few places where pointers are borrowed.
	Use typesafe unique_ptr variants of json::object::set and
	json::array::append throughout to make types of properties more
	explicit, whilst using "auto" to reduce typing.
	Use "nullptr" rather than "NULL" throughout.
	* diagnostic-format-sarif.h (make_sarif_logical_location_object):
	Use std::unique_ptr for return type.

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