Swap QA: Reduce number of decimals we render

The instances where these rendering would disrupt the consistency of the UI and potentially its comprehension: https://www.figma.com/file/VVjoLHG6X74lXmh6CN3r7H/Swaps?node-id=1247%3A0
cc @jakehaugen -- what're the guidelines we should use?

Note - this might break consistency from how we render numbers across the mobile app. We should improve how we render numbers across the app (including internationalization), but that is out of scope for this issue. cc @wachunei

Start by reviewing the linked Figma design and the issue's discussion about guidelines for decimal rendering; no source file, test, or entry point is named. Confirm the intended rendering rules before locating the affected mobile UI, and consider the work complete when the specified Swap values match the design without taking on the explicitly out-of-scope app-wide internationalization changes.

Written by the indexing model from the issue text.