Fix fs-verity per fs-verity spec change

- Reorder and adjust fields per fs-verity format change.
- Since header + tree is no longer full page size, pass the length with
  shared memory (which is full pages).
- Fix offset and padding of patch extension.
- It is now required to issue the measure ioctl (via
  assertFsverityRootHashMatches) right after fs-verity is enabled.

Test: adb install a new priv app, saw fs-verity log in dmesg. Read the
      whole file successfully.
Bug: 30972906
Change-Id: I480ae2b5debaf76ef24dadf2d79d1903c7967f03