Fixes#155552
For lists, the outer ul/ol always has the same source line as the first element in the list. We should prefer using the first element in the list when highlighting the active line
This also fixes a bug where scroll sync would stop working if you added lines to the doc. This was caused by `lineCount` getting out of sync as the document is being updated. I've removed this state and made the reveal logic more robust instead
* fonts - adopt monaco-monospace-font in more places and make it consistent
* font - use platform specific fonts in more places
* font - move system-ui before Ubuntu font in places where we cannot control platform
* font - only use system-ui on Linux
* fonts - adjust font stack for other windows
Sets the tab size to 4 in the Markdown preview for code blocks in Markdown documents. I consider a tab size of 4 being standard and the default of 8 being unbearable. The few people, if any, using a different tab size than 4 can use the custom markdown preview style feature, if it is going to be fixed anytime (https://github.com/microsoft/vscode/issues/77290).
[`tab-size` is still marked *experimental* in the MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/tab-size), but it doesn't hurt, if not supported. However, in the used Chromium version it is supported.
