More android.os work for Ravenwood, with CTS.

Bring along simple UID math utility methods, and the ability to
detect 32-vs-64-bit environments.

Bug: 292141694
Test: atest-dev CtsOsTestCasesRavenwood CtsOsTestCases
Change-Id: I5f3841dbe5cae703facc9020ba8c5405aa3ebcae