Previously, Magisk uses persist or cache for storing modules' custom
sepolicy rules. In this commit, we significantly broaden its
compatibility and also prevent mounting errors.
The persist partition is non-standard and also critical for Snapdragon
devices, so we prefer not to use it by default.
We will go through the following logic to find the best suitable
non-volatile, writable location to store and load sepolicy.rule files:
Unencrypted data -> FBE data unencrypted dir -> cache -> metadata -> persist
This should cover almost all possible cases: very old devices have
cache partitions; newer devices will use FBE; latest devices will use
metadata FBE (which guarantees a metadata parition); and finally,
all Snapdragon devices have the persist partition (as a last resort).
Fix#3179
16e4c67992