Add Handle::GetFromGdb function

When using a debugger it is normally quite difficult to examine
mirror objects being held by Handles due to the inlining of the
various accessor functions. This adds a new 'GetFromGdb' function that
is emitted normally to allow one to decode the handle from gdb. This
function is defined for every Handle type using a macro.

Test: Manual debugging
Change-Id: I7cb95468b1a14438df4dccdf84b48e2af5ec71b9
4 files changed