Enhance and flesh out the C++ language options

[MindSwipe]

The current cpluplus.nix is very barebones and is missing a lot of stuff. I'd love to see a handful of things, namely exposing a handpicked set of compilers, language server implementations and build system, while exposing the ability to set a custom one for each. I'd likely structure this like the javascript.nix module does it.

This is something I'd be willing to work on.

[domenkozar]

See #1974

[MindSwipe]

Ah cool. I won't spend more time on my rewrite then.

[sandydoo]

Ah cool. I won't spend more time on my rewrite then.

@MindSwipe, we want to introduce a common/predictable structure for setting up language components (hence #1974), but we could always use input on the language-specific parts: default compilers, LSP tools, formatters, additional toggle-able tools, etc.