Android: Add SDK extension library for Android XR

Bug: 390751822
Change-Id: Ic81d70b62234dcb9d00fc709a293fe159fb290a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6289295
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1423357}
NOKEYCHECK=True
GitOrigin-RevId: 2e9bdbf2c8aa65455ba65f017c45ebfa532fd0e3