Use new AndroidUnwinder object.

Replace libbacktrace with the new AndroidUnwinder object.

Bug: 120606663

Test: Ran unit tests.
Test: Added call of UnwindMainThreadStack() in DebugRebootLogging()
Test: and verified unwind data is logged properly.
Change-Id: Ia724f9485377d6d2c894283242a3c5653bf82768