Support redaction and ContentResolver#open with passthroughHEADlineage-18.1

With FUSE passthrough enabled we can simplify the following policies:

1. Redaction: Always use passthrough for open(2) without redaction and
non-passthrough for open(2) with redaction. This works because
different VFS page caches are used for passthrough vs non-passthrough.

When passthrough is disabled, we still use the policy introduced in
I6eb1903ee22b8d713fe792ad8fef457a140e91f1

2. ContentResolver#open: All opens go through the FUSE filesystem,
this avoids the page cache inconsistency problems entirely! Hence, we
don't need any delicate file-locking algorithm to keep the cache
consistent.

Note that we still have to handle the dentry cache inconsistency
problems from unlink(2)/rename(2) within MediaProvider.

When passthrough is disabled, we still use the policy introduced in
I7726a75a51869c0e3ea3856103dd501b1aa19d14

Bug: 168023149
Test: atest ScopedStorageCoreHostTest#testVfsCacheConsistency
Change-Id: I8927cfb16f82578c9062036b3b46ad238e408ce6
Signed-off-by: alk3pInjection <webmaster@raspii.tech>

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