[camerax] Small fixes to starting/stopping video capture

[camsim99]

Fixes small issues I noticed in starting/stopping video capture while working on #6059, notably:

• Change all remaining unawaited calls to await to avoid any racy behavior.
• Update camera info after VideoCapture use case is bound to the lifecycle of the plugin's ProcessCameraProvider to make sure it is up to date.
• Unbind VideoCapture use case when video recording stops since it was suggested to lazily load it for performance reasons (open to pushback on this). this would require potentially more changes than I originally thought
• Make tests checking that async methods throw exceptions actually wait for those exceptions as this may cause flaky test behavior.

Fixes flutter/flutter#132499 as this PR removes any remaining unawaited calls.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

[gmackall]

LGTM with only comment being, do we often put issue links in changelogs? If so then carry on, otherwise replace with a description of what is being solved

[camsim99]

LGTM with only comment being, do we often put issue links in changelogs? If so then carry on, otherwise replace with a description of what is being solved

Ah Reid recommended this for another PR but that's the only time I've done it. I have no prob just writing the fixes out, though, so I can do that :)

[camsim99]

@gmackall I assumed that unbinding VideoCapture would work based on our original lazy loading philosophy but it actually is causing errors, so I'm going to revert that change. If you think it's worth exploring further, I can file an issue, but I'm okay leaving as is since it still will not be loaded until it is used. I assume the issue comes somewhere from setup I didn't include (like dealing with the Recorder, Recording, etc.)