Triangle CN prove version

[Crisforlove]

Overview: What does this pull request change?

Added a Chinese version of a demo that proves the sum of the interior angles of a triangle. Two methods are demonstrated to prove this fundamental geometry concept.

Motivation and Explanation: Why and how do your changes improve the library?

This PR introduces a Chinese-language demo proving the sum of the interior angles of a triangle. It offers two methods for users to explore, enriching the educational content of the library and providing a more accessible version for Chinese-speaking users.

Links to added or changed documentation pages

Further Information and Comments

The demonstration showcases two distinct methods to prove that the sum of the interior angles of a triangle equals 180 degrees. This adds value to the educational materials in the Manim community, particularly for those who prefer or need content in Chinese.

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

[JasonGrace2282]

Hey, thanks for your interesting in contributing to Manim!
We appreciate your enthusiasm for adding documentation (it is something that can always be improved!), and especially for adding it in a non-english language.
However, I'm not sure if a separate example in Chinese is the right way to go with this. Manim has a system for adding translations in other languages, so maybe some documentation examples in English, followed by an i18n translation into Chinese is a better way to go?