rP761134a1a9fe

Line counters: do not wrap when over 999 on mobile

Summary:
| Before | After |
|-----------|-----------|
| {F335620} | {F335621} |

Closes T15615

Test Plan:
Create a very long Diff with soooo much lines (e.g. 1000+).
Reduce the window and check that line numbers do not wrap anymore.

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15615

Differential Revision: https://we.phorge.it/D25407