Pause watchdog triggering on the main thread during package scan

Similar to I3876c41e6d0e41d044a5b1d5e57f894c7fb4fb0e and
I69067fbbb8be4e421918c18b67269044fab51b3e where we pause
the watchdog because dexopting and moving A/B artifacts can take a while,
here scanning packages can take a long time depending on the number of
apps installed on the device.

Bug: 135103243
Test: Manually tested by adding an artificial sleep in
PackageManagerService#main and verified that watchdog was not triggered

Change-Id: Ia5b2b5741194a33f7cd09e79c0904696ce546026
Merged-In: Ia5b2b5741194a33f7cd09e79c0904696ce546026