This fixes an issue where due to the scrollbar appearing, the reported
content size would shift, causing issues in the process. We now actually
always reserve space for the scrollbar appropriately as described in
https://github.com/zed-industries/zed/pull/33636 initially.

Release Notes:

- Fixed an issue where the scrollbar could cause a layout shift in the
terminal.

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>