Unify Monaco themes
Created by: lguychard
Fixes #7697 (closed)
It is currently not possible to have two Monaco editors have different themes: https://github.com/microsoft/monaco-editor/issues/338
This caused conflicts when displaying the settings editor on the same page as the Monaco-backed search field. This PR unifies our Monaco themes. The main resulting difference is that in settings editors, hover tooltips will integrate better with our existing theme.