[camera] adding freeze parameter to CameraPreview

[nt4f04uNd]

fixes flutter/flutter#75751

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[nt4f04uNd]

this is wip, as it's blocked by other issues, see flutter/flutter#75751

[nt4f04uNd]

i'm wondering if this is good thing though, because when flutter/flutter#75750 and the camera controller buffer will be exposed as per last bullet in here flutter/flutter#31225, won't be freeze redundant? for example for the use case i listed in the flutter/flutter#75751 it will work faster, but there's a chance that it will be not accurate
so, in general i'm not sure about this change

[nt4f04uNd]

@cyanglaz i guess it's ready for review