Improve syntax highlighting

[mirnovov]

Thanks for making this extension - nice work! However, I've noticed several flaws in the provided syntax highlighting. This PR fixes and/or improves the handling of:

• Generics with multiple parameters in function arguments, struct members, and definitions
• Generics with the Rust empty type ()
• Variables that are assigned after initialisation
• const and static members (as part of this, lets are not shown as constants anymore, let me know if you want to revert this)
• Struct members without a trailing comma
• pub struct members
• Pre-sized arrays
• Raw pointers
• Numeric values

[kilbd]

Thank you so much for your contribution!

I mentioned in the extension details that I'm still learning Rust and there's probably a lot I've missed or gotten wrong, so I and other Nova users truly appreciate your help.