Overview: support for SVG features

[behackl]

There are a bunch of SVG features that appear more or less regularly that Manim currently does not support. Missing features that have been reported at some point are collected here.

• <image>-tag (-> ImageMobject?) -- Increasing Latex compatibility to make Manim more powerful #3577
• <text>-tag (-> Text or MarkupText?) -- SVGMobject doesn't display svg image properly #1561
• Patterns -- SVG support as a fill pattern. #2944
• Gradients -- SVGMobject / manim doesn't support linear gradients #2112