Use AtomicFile in UpdatableFontDir.

Also add more precondition checks.
Bug: 186785560
Test: atest FrameworksServicesTests:UpdatableFontDirTest
Test: atest UpdatableSystemFontTest

Change-Id: I4edaf1d2f6dcc9de1f0b1adc7db4a83a76d5f2a2
3 files changed