Add <staging-public-group> tags to T

To prevent apps from having to respin atomically with SDK finalization,
<staging-public-group> must be created with type ids that do not
overlap the public resource id namespace.

For SV2, start allocating type ids at 0xff and decrement to get
additional type ids. For T, start allocating type ids at 0xdf. The type ids
for an API level do not have to be next to each other, but to make
potentially adding new types to SV2 easy, this change leaves a gap of
14 type ids between the end of the SV2 staged type ids and the
beginning of the T staged type ids.

Continuing this pattern will allow for approximately 7 releases before
new <staging-public-group> tags need to start over at 0xff.

Bug: 188463919
Test: builds
Change-Id: Ia7835d04d988127d061d3a454b8391294346a915