Added type annotations to mobject/svg/brace.py

[henrikmidtiby]

Overview: What does this pull request change?

Type annotations were added to the brace.py file.

Reviewer Checklist

• [ ] The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• [ ] If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• [ ] If applicable: newly added functions and classes are tested