[camera_android_camerax] Support NV21

[camsim99]

Implements NV21 support for image streaming.

Also bumps the CameraX version to 1.5.0-rc01! To do this, I needed to (1) bump the minimum SDK version to 23 and (2) modify a couple of unrelated tests.

Fixes flutter/flutter#145961.

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[camsim99]

I notice that the diff here is a bit funky....it might be easier to look at the file itself and search for the tests that I modified there. I really only:

1. Modified tests that tested logic previously in createCamera that I moved to initializeCamers
2. Added createCamera and initializeCamera properly set filter for resolution preset for non-video capture use cases and initializeCamera sets camera state observer as expected.