[Feature Request] More Scaling Filter

[Ichisich]

Related to https://github.com/easymodo/qimgv/issues/425#issue-1293056866

Depending on the use case, the nearest-neighbour, bilinear and bicubic filter, all can have noticeable drawbacks. On a subjective level, I would recommend implementing at least Spline36 (Sharp) and Mitchell (artefact free, especially useful for downsampling).

P.S. Currently, the toggleScalingFilter shortcut only cycles between the nearest-neighbour and the bilinear filter.