[sgen] Cleanup, remove object ranges for finalization and weak link code, they no longer are needed.
[sgen]Rework the ephemeron code to not rely on object ranges and make sure it works with split nursery.

	* sgen-gc.c (sgen_is_object_alive): Extract sgen_major_is_object_alive function.

	* sgen-gc.c: Add sgen_is_object_alive_for_current_gen and sgen_is_object_alive_and_on_current_collection
	functions that handle old objects during nursery collections as either all live or all dead.

	* sgen-gc.c (sgen_object_is_live): Use sgen_is_object_alive_and_on_current_collection which is more
	robust, handling to-space nurseries and pinned/evacuated old gen objects. Bridge now works with those.

	* sgen-gc.c: Get rid of heap range for the ephemeron functions and use sgen_is_object_alive_for_current_gen
	which produces the same result, which is treat all old gen objects as alive during a minor collection.

	* sgen-gc.c (clear_unreachable_ephemerons): Don't add remsets for elements on arrays they are not really needed
	since we scan all ephemerons on all collections.