Mount + leverage rootfs lacros-chrome (over stateful/component lacros)

When:
 1. the stateful lacros-chrome is missing
 2. the stateful lacros-chrome version is <= rootfs lacros-chrome.

This allows lacros-chrome to be quickly mount + loaded without waiting
for the stateful lacros-chrome to be downloaded.

The stateful lacros-chrome will be installed/update even when rootfs
lacros-chrome is used to always use/be up to date with the latest
version of lacros-chrome.

Pseudo logic
```
if no stateful || stateful.version <= rootfs.version:
  use rootfs && install/update stateful
  return
use stateful
```

BUG=183436593
TEST=# deploy_chrome + verify rootfs lacros-chrome works.
TEST=# Verify that the stateful lacros is installed/updated
TEST=# even when rootfs lacros-chrome is used.

Change-Id: I3a0cdfdaa1f03b6dcd6d2aa660c58a25d056a835
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2896239
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#884233}