Support Advanced Hovers

Summary of the new feature

The existing powershell hover for commands/functions is very basic and only provides the synopsis. VScode now supports colorized advanced hovers, and Omnisharp C# extension already implements this as a reference.
https://code.visualstudio.com/api/language-extensions/programmatic-language-features#show-hovers

Powershell should support the same for functions and methods, displaying colorized syntax info about the function, and ideally not just the synopsis but parameter descriptions. The verbosity could be controlled via a setting.

Proposed technical implementation details (optional)

This should be done after the parser rewrite. It should probably be tagged a good-first-issue as well, I'd be willing to give it a shot once the parser rewrite is done to avoid a moving target.

This could also be a good candidate as a separate extension for the extension API that @TylerLeonhardt was working on, though it may be difficult to make sure the two don't clobber each other.

No repository files or tests are named. Start after the parser rewrite by reviewing VS Code's programmatic hover documentation and the Omnisharp C# implementation, then inspect the extension API proposal mentioned in the issue. Done means functions and methods expose colorized syntax, synopsis, and parameter descriptions with controllable verbosity without clobbering another extension.