ios camera takes advantage of NV12 pixelbuffer

[cikelengfeng]

iOS takes advantage of 420v pixelbuffer

In order to make it more convenient for everyone to use the gain brought by this PR, I modified the camera plugin to enable it to output the pixelbuffer in NV12 format (of course, this is turned off by default)

Related Issues

flutter/flutter#31041

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[danielroek]

@cikelengfeng Would it be useful to have a option exposed to Dart where users are able to choose which videoFormat to use? e.g. a boolean use420Y, which defaults to false. Now users do not have the option to use it, as they would have to clone the camera plugin to change the line of code u added.

[mvanbeusekom]

This feature is implemented in #3359, therefore closing this PR.