stack::btm:: Consolidate test fixtures btm_test_fixtures.h am: c1c9d309 am: 2d9ce4c1

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Bluetooth/+/3025505



Change-Id: Iff63911e0649d642f6cc9a8038c284ce56a3ada3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>