Fix exporting animation frames into EXR format
The patch fixes two problems:
- DlgAnimationRenderer didn't initialize frames' mimetype correctly, so exporting always happened into PNG format.
- DlgAnimationRenderer should correctly initialize saving format settings from the default cfg.exportConfiguration(). Using the same settings for both, animation rendering and normal image save is a disputable approach, but that is how we do it for ages.
- EXRConverter shouldn't call any blocking functions on the image (and shouldn't change the state of the image as well). So it should convert non-16f/32f layers on the fly.
BUG:406830