Generate custom icon set as custom font

[achou11]

Related to #979, which fixes an issue related to icon names changing due to dependency upgrades. Determining these breakages is generally tedious so it would be helpful to only extract a subset containing the ones we use

From Gregor:

Would probably be good at some point to generate our own icon set as a custom font, extracting the icons we need from these packages. It would reduce the bundle size and also remove the chance of icons being removed / changed in a way that we can't control.