Dump binder proxies interface descriptors on a separate thread.

There are apparently some processes that block getInterfaceDescriptor()
from completing, thus locking up the thread doing the binder proxy dump.
This can cause the watchdog to restart system_server. Move the calls to
a separate thread and give it some time to complete!

Bug: 174722615
Test: adb shell am dump binder-proxies
Change-Id: Ifa79e53524197bf1d785210b7504e7f6c6ddc9b7