Problem:
If `CompletionItem.documentation` is populated but `detail` is not, then
`detail` is not resolved.
Solution:
Ensure that we resolve a `CompletionItem` if either `detail` or
`documentation` are not populated.
I've also removed `detail` from the popup menu since otherwise it will
be populated in both the popup menu and the info popup after the
`CompletionItem` has been resolved. I think the info popup is the best
place for it anyway as when there is a completion item with a long popup
menu entry (when `detail` is a medium/long function signature for
instance), the whole popup menu gets widened and this steals horizontal
space that could be used to display the `documentation`. Now with
`detail` and `documentation` in the info popup, they share the same
horizontal space. This also aligns with how VSCode, nvim-cmp, blink.cmp,
and mini.nvim display `detail`.
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