Add new link button hidden on hover

Per https://meta.trac.wordpress.org/ticket/6991

When creating a link, the apply button is hidden on hover.

https://github.com/Automattic/blocks-everywhere/assets/767313/3d355e71-d023-4a0f-a81e-b796bdbc1123

It appears this might be an upstream issue in Automattic/isolated-block-editor, but as I can't test that right now, and [we've got modifications](https://github.com/Automattic/blocks-everywhere/blob/trunk/src/styles/theme-compat.scss#L226-L248) for the link editor in this repo, I'm filing here for now.

Code in question that causes it:

https://github.com/Automattic/isolated-block-editor/blob/fca1871c106f68f3926c479afda6b0aa1c6551a0/src/components/block-editor-container/style.scss#L94-L106

Reproduce the link-creation flow and inspect the hover behavior in src/styles/theme-compat.scss, especially lines 226-248. Compare it with the referenced isolated-block-editor rule in src/components/block-editor-container/style.scss, then confirm that the apply button remains visible when hovered.

Written by the indexing model from the issue text.