Added ability to remove non-svg LaTeX files

[JasonGrace2282]

Overview: What does this pull request change?

• Made manim auto-remove non-tex and non-svg files by default. This behavior can be prevented with the CLI flag --no_latex_cleanup
• Made manim check if an svg for a TeX expression already exists BEFORE creating .aux, .dvi, and other files.
  • This makes sure that even the user already has the svg for an expression and runs their code with --no_latex_cleanup, they will not get cluttered with the .aux, .dvi, and other files for that expression.

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

Often, for big manim projects, the media/Tex folder can get quite full with uneeded files. This PR gives users the option to have manim delete these files automatically, instead of having to manually delete said files.

Further Information and Comments

This will automatically delete ALL files without the .tex or .svg suffix in the media/Tex directory. It will only perform this if Tex or MathTex is used and the CLI flag --no_latex_cleanup has not been passed.

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

[uwezi]

I would not remove the .tex file itself. I don't know if it is needed for the caching algorithm, but anyway, it's quite useful for debugging.

[JasonGrace2282]

@uwezi I have modified the code to fit your suggestion :)

(For anyone looking at this [weird] commit history, I had a bunch of weird merge problems)

[JasonGrace2282]

I will move these changes from scene.py and scene_file_writer.py to tex_file_writing.py.

[behackl]

I think there is a bit more here to do; I've left some comments, please take a look. Thanks for your work!