Improve new window & letterboxing dimensions

Meta issue for our various letterboxing issues we should fix in 13.0 stable:

~~Change the default start window size from 1000x1000 mullvad-browser#175 (moved)~~ (duplicate of the below ticket)
Increase max width of new windows #33282 (closed)
Re-evaluate letterboxing dimension choices #30556 (closed)

Let's plan on doing this work in base-browser so tor-browser can get these improvements also.

Edited Aug 08, 2023 by ma1

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