Reduce concurrent issues of WmTests

Wait for the async initialization of PerfettoProtoLogImpl to
avoid breaking mocking operation by concurrent access.

Also only initialize once to avoid leaking the threads created
by mBackgroundLoggingService.

Bug: 395656832
Flag: EXEMPT TEST_ONLY
Test: WmTests

Change-Id: Ib3387e9f03c2dd7e892e6cf5dea2c328575bdad4