Apply React editor font styles via CSS instead of inline styles

/cc @benogle 

Previously, editors always assigned their font styles inline based on the config settings. We then had some mini-editor-specific styles for the line height and opted out of setting the line height inline for mini editors only. This was kind of a confusing mess.

This PR updates the editors to behave just like ordinary HTML elements, using whatever the computed font styles are on the root editor element as the basis of our rendering decisions. The setting of the font size, font family, and line height is now moved to a global stylesheet that is managed by the workspace view. This will allow us to style mini editors (or any other editor for that matter) in a manner specific to its context with normal CSS.

This sets us up for the last step before switching to React-based mini editors, which is @benogle fixing the styling in key locations where mini editors are used.
There are multiple editors, but this applies to all of them. I wanted a singleton instance.