3DS: Improve sharpness of non-integer scaling modes.
[This is what we do in the TIC-80 port.](https://github.com/nesbox/TIC-80/blob/master/src/system/n3ds/main.c#L390-L403)

I use the GPU (which is not very busy, admittedly) to scale the 240x136 TIC-80 display to 720x408 (3x integer), then scale that down as necessary. This improves the sharpness of the resulting non-integer scaled output.

This helped sharpness in our case; I am not sure how much it will help with FAKE-08.