Closes https://github.com/zed-industries/zed/issues/31565

* Looking up settings on every row was very slow in the case of large
folds, especially if there was an `.editorconfig` file with numerous
glob patterns
* Checking whether each indent guide was within a fold was very slow,
when a fold spanned many indent guides.

Release Notes:

- Fixed slowness that could happen when editing in the presence of large
folds.