Use VSCode product icons

[MrCodingB]

I think the icons in the title bar don't really fit in with the default look of VSCode.

It would be better to use the native product icons, to achieve a more standard look:

If you use the debugger icons (e.g. debug-restart, debug-stop) you could even add some color. Also people could customize the look of the test explorer (or at least the title bar) with product icon packs.

[ImLuze]

@hbenl I can have a shot at this issue if you would wish to proceed with this.

[ghost]

There is a PR, also waiting for that :)