Support Handler/Looper for Ravenwood, with CTS.

Now that we have a solid foundation of classes available, one of the
tricker pieces is supporting Handler/Looper under Ravenwood.  At its
core, the native implementation of MessageQueue can be emulated using
core JVM primitives, which is enough to reliably pass CTS.

Advanced features like FileDescriptor events will need to wait until
we eventually have real JNI support.

Fix obscure bug with SystemClock; must be positive number.  Always
start our "fake" pointers from 1 to prevent `nullptr` oddness.

Bug: 292141694
Test: atest-dev CtsOsTestCasesRavenwood CtsOsTestCases
Change-Id: I0f82b659973443968ef2609a7e3151f381abff29