[Cashtab] Renamed FormItemWithMaxAddon

Summary: Renamed FormItemWithMaxAddon, related to task T2059

Test Plan:
cd web/cashtab
grep -r 'FormItemWithMaxAddon' src/
ensure there are no instances of this being used in the app

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10641