[camera_android_camerax] Restore torch state when camera changes

[camsim99]

Continuation of #12302..

Restores the state of a camera when that camera was previously initialized. For example, if you initialize camera A and start the torch, then initialize camera B, then switch back to A, the torch will turn off when camera B is started but then turn back on when switching back to camera A.

Fixes flutter/flutter#160956.

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[camsim99]

Sometimes there is more than a front/back camera. Should we consider saving a mapping of the camera to the torch state to account for this versus a single bool?

[camsim99]

Yes, typo!