[camera_avfoundation] Wrappers swift migration - part 4

[RobertOdrowaz]

Migrates camera wrappers as part of https://github.com/flutter/flutter/issues/119109

This PR migrates wrappers to Swift:

• FLTCaptureConnection
• FLTCaptureDeviceFormat
• FLTAssetWriter

In line with Swift conventions, the FLT prefixes are removed. The Default class implementations are replaced with protocol conformance on base AV classes.

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[RobertOdrowaz]

@hellohuanlin pls take a look at this PR again when you have some time

[hellohuanlin]

Is this ready for another pass?

[RobertOdrowaz]

@hellohuanlin It's ready now. I've reverted the error handling and will open an issue once this is merged

[RobertOdrowaz]

@hellohuanlin pls take a look again when you have some time

[hellohuanlin]

Sorry, I have been working on an urgent bug. Will take a look later this week.