Adjust function-call fontification in csharp-ts-mode (bug#60376)

Adjust function-call fontification in csharp-ts-mode (bug#60376)

- Ensure method-invocations are highlighted only on level 4.
- Ensure consistent fontification of variable declarations
  (don't highlight usage of all variables).
- Fix issues with highlighting types in new() expressions.
- Fix issues with generic types in variable-declarations not using "var".
- Use fewer, more general queries for function-invocations. simplify code.

* lisp/progmodes/csharp-mode.el (csharp-ts-mode--font-lock-settings):
Change rules.
(csharp-ts-mode): Update feature list.