Document the text attribute mappings in the Text initializer

[harlanhaskins]

Overview: What does this pull request change?

This adds documentation comments for the t2c, t2f, t2g, t2s, and t2w, and documents their long-form names. It also adds more specific type information to t2c and t2g.

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

These were undocumented and it was difficult to find out what to provide within them outside the bounds of the specific examples.

Links to added or changed documentation pages

https://manimce--4086.org.readthedocs.build/en/4086/reference/manim.mobject.text.text_mobject.Text.html#manim.mobject.text.text_mobject.Text

Further Information and Comments

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