[Desktop] Use DeviceInfo.isDesktop() instead of BuildConfig.IS_DESKTOP_ANDROID for runtime checks in Java.

Note:
* Further changes needed to use DeviceInfo check in runtime checks in c++ code.
* BuildFlag IS_DESKTOP_ANDROID will still be used to isolate components during compile time.

Make AutomotiveContextWrapperTestRule more generic and rename it to
OverrideContextWrapperTestRule. Also includes a function to set the
Desktop system feature.

Change-Id: I9cceaa4f04976b811cd80f6e20bc359f5071f4fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6685287
Auto-Submit: Sirisha Kavuluru <skavuluru@google.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Sirisha Kavuluru <skavuluru@google.com>
Cr-Commit-Position: refs/heads/main@{#1481837}