add 128 x 128 png/bmp of icon

[donaldguy]

For no particularly clear reason I just spent several hours adapting the 32x32 px bitmap from https://raw.githubusercontent.com/RamonUnch/AltSnap/main/media/icon.ico into a smoother 128 x 128px version, as:

• From the original:
  

1. Added back the 2 pixels missing for ~no reason (possibly from original downscale of uncommitted file?); then de-cropping to 33 x 33 and finishing the bottom and right arrow tips:

   ->

2. moving up to 35x35 and making some separation between the two element

   

3. I then looked at some automatic upscale approaches to 128x128 (see alt text) all of which were probably sufficient

        

4. Then I accidentally spent like another 3 hours doing a hand edit starting from the nearest neighbor version (As though I were making sprites / pixel art; there were probs faster ways):