Port recent improvements to SVGMobject, CodeMobject etc from 3b1b/manim

[behackl]

Enhancement proposal

SVGMobject and some related mobjects (Text, CodeMobject) have recently been refactored and improved substantially over at 3b1b/manim. It would be a good idea to check in how far these changes could be ported over.

Relevant PRs:

• Attempt to refactor SVGMobject with svgelements 3b1b/manim#1731
• Reorganize inheriting order and refactor SVGMobject 3b1b/manim#1745
• Refactor Text with the latest manimpango 3b1b/manim#1751

[naveen521kk]

I would say not to port over 3b1b/manim#1751 (I would be working on the new text API soon), others yeah it's good to have.

[YishiMichael]

Recently I've finished refactoring MTex, MarkupText, both of which inherit from StringMobject, a newly-constructed ABC. I'd like to hear some suggestions from Manim Community, and seek for possibility to port it over here.

See PR here:

• Refactor StringMobject and relevant classes 3b1b/manim#1795

[naveen521kk]

For any changes in Text/MarkupText waiting for #2355 is a great idea. It would be great if you could help out with how it would work with the API proposed there.

For the MTex/Tex you can open a PR and we'll discuss it there. Thanks for your contribution!