Baseline `StrictMode` on Ravenwood.

We've uncovered several utilities that temporarily clear any
read/write thread policies.  Instead of making them all side-step
their StictMode interactions on Ravenwood, this change offers just
enough of a baseline implementation to support them; it doesn't
actually offer to detect anything.

Bug: 318833612
Test: atest FrameworksCoreTestsRavenwood
Change-Id: I5e406e24fcd5e83d108006ca6c7d08c0534297a9