Previously FuseAppLoopCallback needs to return values in a synchrnous
manner. The CL changes it to asynchronous mannger so that apps can
process FUSE message asynchrnously.
Bug: 35229514
Test: FuseAppLoopTest
Change-Id: I8edcfdb003a25cfd5e9c490ec871140220b21e35
(cherry picked from commit f5d15f9fc4)
The class is used at the app side (StorageManager) to parse FUSE
commands.
Bug: 32260320
Test: libappfuse_test
Change-Id: I1ae2904d3290a041f1efbf8fc10ba032eda5449c