gpui: Move generic bounds to a `where` clause for better readability (#23985)

This PR moves some generic bounds to a `where` clause to improve the
formatting/readability of the associated `impl` block.

Release Notes:

- N/A
7bf4fd6c46Marshall Bowers committed on 1/30/2025, 11:10:05 PM· committed by GitHubparent2c950cf
1 file changedLine totals unavailable