json: support std::unique_ptr in array::append and object::set

json: support std::unique_ptr in array::append and object::set

This patch uses templates to add overloads of json::array::append and
json::object::set taking std::unique_ptr<T> where T is a subclass of
json::value.

Doing so makes it much easier to track memory ownership and enforce
schema validity when constructing non-trivial JSON; using the wrong
kind of JSON value leads to compile-time errors like the following:

error: cannot convert ‘unique_ptr<sarif_message>’ to ‘unique_ptr<sarif_log>’
  629 |   location_obj->set<sarif_log> ("message", std::move (message_obj));
      |                                            ~~~~~~~~~~^~~~~~~~~~~~~
      |                                                      |
      |                                                      unique_ptr<sarif_message>

No functional change intended.

gcc/ChangeLog:
	* diagnostic-format-json.cc: Define INCLUDE_MEMORY.
	* diagnostic-format-sarif.cc: Likewise.
	* dumpfile.cc: Likewise.
	* gcov.cc: Likewise.
	* json.cc: Likewise.  Include "make-unique.h".
	(selftest::test_formatting): Exercise overloads of
	array::append and object::set that use unique_ptr.
	* json.h: Require INCLUDE_MEMORY to have been defined.
	(json::object::set): Add a template to add a family of overloads
	taking a std::unique_ptr<JsonType>
	(json::array::append): Likewise.
	* optinfo-emit-json.cc: Define INCLUDE_MEMORY.
	* optinfo.cc: Likewise.
	* timevar.cc: Likewise.
	* toplev.cc: Likewise.
	* tree-diagnostic-client-data-hooks.cc: Likewise.

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