Audio focus: fix delayed focus request during locked focus behavior

Fix issue where if audio focus was requested with GAIN, and
accepted delayed focus, while focus was locked, then previous
focus owners didn't receive LOSS, and thus would be removed
from the stack.
 The fix consists in propagating the focus loss through the
stack under the focus locker, and remove any focus loser
if the loss was definitive.
 In order to simulate the bug conditions, the test API for
simulating focus requests and abandons, was modified to support
locking the focus like in a phone call.

Bug: 206856107
Test: atest AudioFocusTest#testAudioFocusDelayedByCall
Test: atest AudioFocusTest#testAudioFocusTransientDelayedByCall
Change-Id: I211cd46b66c882499bfa43718bc0cb37b2f79817