[camera_avfoundation] Implementation swift migration - part 5

[RobertOdrowaz]

Migrates camera implementation as part of flutter/flutter#119109

This PR migrates a part of FLTCam class to Swift.

This PR includes the second chunk:

• start
• stop
• close
• receivedImageStreamData
• reportInitializationState
• setExposureMode
• setExposureOffset
• setExposurePoint
• setFocusMode
• setFocusPoint

Some properties of the FLTCam have to be temporarily made public so that they are accessible in DefaultCamera.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• 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 I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[RobertOdrowaz]

This PR falls under the "refactors with no semantic change (e.g. null safety migrations)" test exemption. It's a part of the migration from ObjC to Swift so by design it's covered by the existing tests

[hellohuanlin]

@RobertOdrowaz Please request an exemption in Discord channel.

[stuartmorgan-g]

test-exempt: code refactor with no semantic change