More Overall Visual Consistency with Xcode

[austincondiff]

We seem to generally be following the editor visual style of Xcode. There are a few things that need to be addressed to get be more visually consistent. (left - Xcode, right - CodeEditorView)

• Better syntax highlighting
• Increased line height
• Smaller and more narrow line number font.
• General editor font styling is off (maybe smaller font size by 1px and increased font weight?).

• General message styling (typography, iconography, colors, animation, dismiss popover button, etc) needs work

[mchakravarty]

Let me address the points in turn:

• Syntax highlighting: Xcode uses a two-phase system. There is the basic syntax highlighting that you'll get right away, and then (with a little delay), you get additional (semantic) highlighting that —I assume— is powered by information from SourceKit. The editor view itself can only do the basic syntactic part, as the rest requires information from a more sophisticated source code analysis (what SourceKit does). My plan is definitely for CodeEditorView also to be able to make use of additional semantic information (like the information provided by SourceKit or LSP), but that isn't implemented yet. This will need a design and one big question is how to represent that information. Make plan so far was to go with what LSP does, but I am open to better ideas.
• The font issues should in the end all be configurable to keep CodeEditorView flexible. I think that will be quite easy to do. On the first go, I simply hardcoded some of these things, because that gave me a faster turnaround. There is already support for themes and these configuration details should probably go there.
• Re message styling, we have Message view display improvements #3.