Test double-loading libbinder.

This is in preparation for the technical possibility of vendor using
libbinder_ndk to communicate w/ Stable AIDL interfaces on system or for
other possible usecases which may use double loaded libbinder.

Bug: 136027762
Bug: 138450837
Test: atest binderVendorDoubleLoadTest
Change-Id: I7b166ae08954283b378e1f18d2c44dcf70e698c5