Monaco improvements (#15333) (#15345)

- Create theme at runtime which follows the CSS variables of the site
- Disable a few opinionated Monaco defaults like minimap and word highlights
- Move styles to separate file

web_src/less/themes/theme-arc-green.less

@@ -106,6 +106,7 @@
   --color-text-focus: #fff;
   --color-expand-button: #3c404d;
   --color-placeholder-text: #6a737d;
+  --color-editor-line-highlight: var(--color-primary-light-5);
 }
 
 .ui.horizontal.segments > .segment {