[camera_android_camerax] Implement setDescriptionWhileRecording

[blackorbs-dev]

setDescriptionWhileRecording allows switching camera while a video recording is in progress

Fixes #148013

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[gemini-code-assist]

Code Review

This pull request implements setDescriptionWhileRecording for the camera_android_camerax package, allowing users to switch cameras during an active video recording. This is achieved by leveraging the experimental asPersistentRecording feature from CameraX. The changes span across the Dart plugin implementation, the native Android (Java/Kotlin) side, and the Pigeon communication layer. Documentation in the README has been updated to reflect the new feature and its usage, and new integration and unit tests have been added to verify the functionality. My review focuses on the core implementation logic and its potential side effects.

[camsim99]

Looks good but I did catch an error I think we should go ahead and fix and test + do the same for the Gemini suggestion. Thanks for all of the hard work! So excited for this to land :)

[camsim99]

Wow thanks for the quick fixes! LGTM :) Just need to resolve merge conflicts.

@bparrishMines for a second review

[bparrishMines]

LGTM

[blackorbs-dev]

I think this PR can be merged @camsim99