We've been allocating task objects without freeing them, oops. We
don't really need full classes for these tasks, so move them to
blocking methods, and invoke them from a detached thread.
Remove FIDTRIM support, which isn't meaningful on UFS-based flash
devices. Modern devices require FBE/FDE which gives us better
protection against trimmed data lingering around.
Rename "Trim" to more generic "IdleMaint", since it'll soon extend
to include custom F2FS optimization logic.
Check for shady ".." when validating paths.
Test: cts-tradefed run commandAndExit cts-dev -m CtsOsTestCases -t android.os.storage.cts.StorageManagerTest
Test: cts-tradefed run commandAndExit cts-dev --abi armeabi-v7a -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.AdoptableHostTest
Bug: 67041047
Change-Id: I4fb194c5d5ef13f413c02acedfbaaf79c567582b
