[camera_avfoundation] Pigeon swift migration - part 1

[RobertOdrowaz]

Prepares camera package for pigeon Swift migration as part of flutter/flutter#119109

Current implementation of FormatUtils.selectBestFormat overrides MediaSettings.framesPerSecond. With swift pigeon contracts MediaSettings is non mutable so that will no longer be possible.

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Code Review

This pull request effectively refactors the camera package to remove its dependency on the mutability of MediaSettings, which is a necessary preparation for the upcoming Pigeon Swift migration. The changes are well-contained and logical, primarily by introducing a local framesPerSecond property in DefaultCamera and making FormatUtils.findBestFormat a pure function. I have one minor suggestion to improve code readability.

[hellohuanlin]

could you explain more about what this means? Is it removing a feature?

[RobertOdrowaz]

It doesn't remove any feature. It's just a refactor, I've described it in the description

Current implementation of FormatUtils.selectBestFormat overrides MediaSettings.framesPerSecond. With swift pigeon contracts MediaSettings is non mutable so that will no longer be possible.

MediaSettings class is generated by pigeon. And when pigeon output is ObjC its fields are mutable specifically framesPerSecond. This field is overwritten as a result of FormatUtils.selectBestFormat execution. When pigeon output is Swift all fields in MediaSettings are declared as let so selectBestFormat can no longer set it. Also in Swift framesPerSecond is an Int64 not NSNumber so it's not possible to assign floating point frame rate to it.