android: add a command script to help display mixed Java/native backtraces.

This script supports displaying developer-focused backtraces when working
with mixed Java and C/C++ stack frames within lldb.  On Android, this represents
just about every app, since all apps start in Java code.

The script currently supports the Art JVM when run on host-side x86_64 and x86,
but does require a patch not yet accepted in AOSP:
AOSP patch: https://android-review.googlesource.com/#/c/106523/

The backtraces will hide Art VM machinery for interpreted and AOT code
and display the Java file/line numbers for Java code, while displaying
native backtrace info for native frames.  Effectively the developer will
get an app-centric view of the call stack.

This script is not yet tested on device-side Art nor is it tested on
any architecture other than x86_64 or x86 32-bit.  Several changes were
needed on the AOSP side to enable it to work properly for x86_64 and x86, 
so it is quite likely we'll need to do something similar for other cpu
architectures as well.

Change by Tong Shen

llvm-svn: 218315