Offer `RavenwoodClassRule`.

Some tests interact with yet-unsupported APIs under Ravenwood in
their test class constructors, and `RavenwoodRule` arrives too late
to effectively apply annotations like `@IgnoreUnderRavenwood`.

This change adds `RavenwoodClassRule` which can be marked as an
`@ClassRule` so that it runs in a static context before each test
class is constructed, giving it a chance to respect annotations.

We also adjust our annotation naming to match the naming style in
JUnit Jupiter, which has annotations like `DisabledOnJre` and
`EnabledOnOs`.

Bug: 319647875
Test: atest SystemUiRoboTests
Test: atest SystemUiRavenTests
Change-Id: I7d834b8e74e961bb3d4befcad6204d99f8fe80e9