authfs: Reorganize modules & rename flags/classes/vars

This change adjusts the module/directory layout to make it easier to
reason.

 - File "transports" are now under file/. Common traits are defined in
   file.rs.

 - All fs-verity related modules are now under fsverity/. This includes
   VerifiedFileReader, which implements traits in the file module to
   provide transparent verification.

 - Rename structs for better consistency.  Drop "Chunked" for
   simplicity.

    ChunkedFileReader          ->  LocalFileReader
    RemoteChunkedFileReader    ->  RemoteFileReader
    FsverityChunkedFileReader  ->  VerifiedFileReader

 - Move and rename get_local_service from remote_file.rs to file.rs.

Also, rename command line flags and related class/field names in main.rs
so that later the name of new read-writable file can fit in more consistently.

New layours:
  src/
  |-- auth.rs
  |-- common.rs
  |-- crypto.hpp
  |-- crypto.rs
  |-- file.rs
  |-- file
  |   |-- local_file.rs
  |   `-- remote_file.rs
  |-- fsverity.rs
  |-- fsverity
  |   |-- builder.rs
  |   |-- common.rs
  |   |-- sys.rs
  |   |-- verifier.rs
  |   `-- editor.rs
  |-- fusefs.rs
  `-- main.rs

Bug: 171279640
Test: atest

Change-Id: Ib257a37df89c6b813f4d97978678db3483d28b57
diff --git a/authfs/src/fsverity.rs b/authfs/src/fsverity.rs
index 37d96c1..1515574 100644
--- a/authfs/src/fsverity.rs
+++ b/authfs/src/fsverity.rs
@@ -16,8 +16,9 @@
 
 mod builder;
 mod common;
+mod editor;
 mod sys;
 mod verifier;
 
-pub use self::builder::MerkleLeaves;
-pub use self::verifier::FsverityChunkedFileReader;
+pub use editor::VerifiedFileEditor;
+pub use verifier::VerifiedFileReader;