Fix watchdog timeout during recomputeComponentVisibility

Due to a held lock, watchdog timeout or lock contentions could occur.

This fix is to remove the lock guard from Computer and make it work
with snapshots.

Bug: 312057281
Test: Manually tested with below steps
      1. Install 2000 packages
      2. Reboot
      3. Make sure watchdog timeout or lock contention doesn't occur
(cherry picked from https://partner-android-review.googlesource.com/q/commit:c788c4cad5740ec21084db2095979d31871daed4)
Change-Id: I40f735924025575477ba24bf35ed3211494159bd