[theming] Access theme's colors programmatically

I think we should add support for accessing theme’s colors programmatically.

For instance let’s take as an example the popular OneDark Pro theme, I’d like to access colors defined under tokenColors.

My use case: I’m making an extension that decorates some tokens, and I’d like them to have the same color that comments have in my theme, the problem is that the regex I use to find those tokens depends on some configurable value, so I cannot pre-compute it in advance and just put it in a .tmLanguage file.

It’s already possible to somehow access colors defined under the colors key, via something like new vscode.ThemeColor ( 'activityBar.background' ), adding support for this sounds like a useful generalization to me.

What do you think?

[vviikk]

A lot of extensions would benefit from this. Bracket colorizer, jumpy, gitlens and a zillion others. Would be good to implement this.

[eamodio]

This issue has come up again. In GitLens, I would like to expose 2 colors (hot and cold versions) for the heatmap that GitLens generates, but I am unable to use theme colors, because I need access to the real color values to generate the full palette of colors required.