libutils: export system_headers

vendor + vendor_available modules built with BOARD_VNDK_VERSION :=
current aren't allowed to use global headers. Since libutils uses
system headers itself, it should export them as well.

Also added some items into windows-deprecated.h. This file is supposed
to be in sync with the libnativewindow variant until all dependencies on
it can be fixed. However, it is missing some updates. This matters when
including libsystem_headers adds system headers before libnativewindow
headers in the lookup paths.

Bug: 33241851
Test: building with BOARD_VNDK_VERSION := current produces many fewer
errors.

Change-Id: I950821f1dae3ddc110db50869247913d5b1aa638