[incfs] Optimized versions of isFullyLoaded()

Create a couple of implementations targeted at specific IncFS
versions, and make them as efficient as it can do.

+ iterate over .index/ directory in v1 incfs when checking for
  full mount, this is faster than recursive traversal

Bug: 183067554
Test: atest libincfs-test
Change-Id: I822d0aef053e1049f017e5ecb717390fe515782b
4 files changed
tree: 181a7aebf603b82a20746576268e7a314c6593b5
  1. incfs/
  2. libdataloader/
  3. sysprop/
  4. .clang-format
  5. METADATA
  6. PREUPLOAD.cfg