styles(explore): Make span description tooltip wider

[Zylphrex]

The default of 225px is too small for some longer span descriptions. Allow span descriptions tooltips to grow up to 400px.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
static/app/utils/discover/fieldRenderers.tsx	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #81084 +/- ## ======================================= Coverage 78.48% 78.48% ======================================= Files 7215 7215 Lines 319793 319837 +44 Branches 44034 44048 +14 ======================================= + Hits 250996 251032 +36 - Misses 62404 62412 +8 Partials 6393 6393 ```