Add syntax highlighting in advanced mode

[alexwkleung]

Adding syntax highlighting to the advanced mode editor would be a nice feature.

I don't think this is extremely challenging to implement, so it might come as part of v0.2.0-dev-4.3.

[alexwkleung]

Small note:

This should be an option and not a forced default. Some enjoy a colourful syntax highlighted editor and some dislike it.

Giving a choice to the users allows ultimate flexibility.

[alexwkleung]

Here's a small preview of what this could look like. Below is Iris in dark mode:

Base from https://github.com/craftzdog/cm6-themes/blob/main/packages/gruvbox-dark/src/index.ts