QCamera API for requesting specific framerate

The Qt QCamera API has no method for setting a specific camera framerate.

Our API relies on the user applying a valid QCameraFormat to control the output of the camera device. This QCameraFormat class contains a range of allowed framerate values. When the user then passes this QCameraFormat class into QCamera::setCameraFormat() our implementations tend to just pick the highest framerate available for this format.

This is problematic when the implementation supports a range of valid framerates for a given resolution and pixel-format. For example, if the device reports a supported format with resolution of 1080p and valid framerate range between 5 and 120 FPS, the user has no option to request 24 FPS.

When we choose a high framerate like this, we give the users less control and we might waste power efficiency on some platforms.