[camera_android_camerax] Allow usage of all use cases concurrently (#10732)

Removes guardrails to avoid previously unsupported concurrent camera use cases (this was changed in a later version of CameraX that came after the guards were implemented. See https://github.com/flutter/packages/pull/6608 for details). Fixes https://github.com/flutter/flutter/issues/150387.

As a bonus, also fixes https://github.com/flutter/flutter/issues/157181 by:

1. Using delayed `Future`s instead of calls to `sleep` which I theorize was blocking calls happening on the native side, so the `sleep` calls were not actually giving time for the camera to initialize
2. Ensuring all calls to start video recording have a delay afterwards to, again, give time for the camera to initialize.

I tracked down these fixes by noticing we actually are not surfacing video recording errors; we actually were getting the [ERROR_NO_VALID_DATA](https://developer.android.com/reference/androidx/camera/video/VideoRecordEvent.Finalize#ERROR_NO_VALID_DATA()) error.  Filed an issue to expose all video recording errors like this for easier debugging in the future: https://github.com/flutter/flutter/issues/182960.

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