Add Features annotations processing to Robolectric tests by default

We should no longer have to add an @Rule using Features.JUnitProcessor
in order to have Enable/DisableFeatures anotations to work.

This cl also fixes tests that relied on the fact that Features
annotations processing was not enabled (thus Features.isInitialized()
returns false).

Bug: 40228727
Change-Id: Id8ac316b4aed27211dbafe1764ccc3be734d8648
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5419671
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Owners-Override: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1285948}