Add tamagui icons

[dnbrwstr]

This PR adds a tamagui Icon component, styled according to latest designs. aCurrently it's only used by the tab nav component.

[alecananian]

Nice! Do we still need the react-native-svg package and all its associated files in the tlon-mobile app code?

[dnbrwstr]

We do still need react-native-svg, since the mobile package is does the actual bundling + rendering of the svg files, but you're right that we don't need the icons or .svgrrc -- I'll remove those. I think it does make sense to keep the svg.d.ts since the typing there will be slightly different than in the web context.