Add formatting of type parameters in class and function definitions (#6161)

Part of #5062 
Closes https://github.com/astral-sh/ruff/issues/5931

Implements formatting of a sequence of type parameters in a dedicated
struct for reuse by classes, functions, and type aliases (preparing for
#5929). Adds formatting of type parameters in class and function
definitions — previously, they were just elided.

crates/ruff_python_formatter/generate.py

@@ -54,6 +54,7 @@ groups = {
     "expr": "expression",
     "stmt": "statement",
     "pattern": "pattern",
+    "type_param": "type_param",
     "other": "other",
 }