Add VmPolicy to monitor path access.

An upcoming StrictMode feature is going to help detect app bugs
where they accidentally interact with credential-protected
filesystem paths while a user is encrypted.

Since much of the existing BlockGuard and BlockGuard.Policy
interface is already on the API greylist, we carefully add a new
parallel BlockGuard.VmPolicy object and start dispatching path
access events to it.  A future StrictMode CL will inspect paths
reported through this interface to report any violations.

Bug: 110413274
Test: atest cts/tests/tests/os/src/android/os/cts/StrictModeTest.java
Change-Id: I98bb9cb428336710566b3a8c81b6332ef981ecfe
4 files changed