init: Allow persistent properties to be written asynchronously.

Persistent properties are flushed with fsync which can cause the
non-persistent property write path to block.

Bug: 250125146
Test: manual test with ro.property_service.async_persist_write = true
Change-Id: Id123bfc7de948b76c51b4d98d00c8cb4a0850bf1
3 files changed