gpui: Always recompute layout on cache miss. (#4131)

I'm not yet sure whether this is 100% correct, but it seems to alleviate
the following issue:
`When opening a dock, the panel doesn't appear right away. An empty dock
is briefly visible.`
Release Notes:

- Fixed panel layout being incorrect for a brief time after opening
(fixes https://github.com/zed-industries/community/issues/2415)
7860372bebMax Brunsfeld committed on 1/18/2024, 10:44:35 PM· committed by GitHubparents93a567a4408d45
1 file changedLine totals unavailable