[ruff_python_ast] Add name and default functions to TypeParam.

[rchen152]

Summary

This change adds name and default functions to TypeParam to access the corresponding attributes more conveniently. I currently have these as helper functions in code built on top of ruff_python_ast, and they seemed like they might be generally useful.

Test Plan

Ran the checks listed in CONTRIBUTING.md#development.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.