authfs: FUSE to serve file with fs-verity verification

The filesystem can currently serve local files specified via command
line flags, with verification using manually specified Merkle tree dump.
It also allows regular read without verification.

The change currently only supports local files for debug only. We will
need to add new configuration for remote file access with our own server
and protocol.

See tools/test.sh for the example setup.

BYPASS_INCLUSIVE_LANGUAGE_REASON=man page

Bug: 173507504
Test: atest --host authfs_host_test_src_lib
Test: tools/test.sh (on workstation)
Change-Id: I0ec14559fe8b4df2bd6fe5888018c12963958dc2
8 files changed
tree: eb0f91f90b83aca2c7b63d8641f910907d5c5aaa
  1. apex/
  2. authfs/
  3. docs/
  4. tests/
  5. .clang-format
  6. PREUPLOAD.cfg