[camera_android_camerax] Fix video recording after backgrounding app (#12145)

Clears the cached recording when `dispose` is called to ensure that the video recording state is cleared when the app backgrounds/resumes. This action does not impact the recording saving; it just updates the state so the plugin knows that the camera is available to start a new recording.

Fixes https://github.com/flutter/flutter/issues/183880.

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Normal pull request information above the line. 

This pull request is an attempt to "oneshot" fixing https://github.com/flutter/flutter/issues/183880. Using Antigravity to execute a plan that is collaboratively worked on. The "rules" are to not allow human authored code to `camera_android_camerax` and to not rely on human code review feedback for code iteration. 

We can add documentation, skills, mcp servers, presubmit test etc. Basically any "support infrastructure" for development is allowed but the package changes must be generated as a single pass. 
When we discover that the plan is not good enough we will blow the package changes away and either modify the plan or add more support infrastructure and try again. 

For more information see the working doc in  [go/flutter-project-one-shot](http://goto.google.com/flutter-project-one-shot).

The agent-authored implementation plan this oneshot was made with can be seen at this commit: https://github.com/flutter/packages/pull/12145/commits/e5f6c954ad52ee687ecbce9cb1b8f438b56d4d44

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