Make repl themable

[aeschli]

I stumbled over repl.css and saw that there are still many colors hard-coded.

Also while at the .css file, it's good practice to qualify all rules with .monaco-workbench (or .monaco-editor) now that the workbench can be embedded in the web.

[isidorn]

Thanks @aeschli for great feedback.
There was some unused CSS, like the .annotation in the repl, so I removed that. I have also now qualifed all with .monaco-workbench.

There is still one hard coded color for .warn in repl, but I believe @robertrossmann tackled this with his great PR. Though I might be mistaken?

[robertrossmann]

@isidorn I did, indeed, add colour contribution points to the REPL as part of #94838 but eventually you asked me to defer those until later, I do not remember the reason precisely... 🤔 So the REPL is still not theme-able, unfortunately.

[isidorn]

@robertrossmann thanks for refreshing my memory.
In case you would like to contribute that part of your PR we are open to accept it now :D
From the .css I only see a need for warn color, not sure if there is more.

[robertrossmann]

@isidorn I am working on this now. ✅

I am taking it a step further, though, and adding theming to most of the REPL elements (errors, warnings, infos, source filenames etc.). Basically I want the whole REPL view to be fully customisable. 💪 🚀