MarkupText: Use Cairo to handle gradients about manimpango HOT 3 OPEN

This will require a refactor in how we render things, see https://gitlab.gnome.org/GNOME/pango/-/issues/533#note_1044494
and corresponding docs https://developer.gnome.org/pango/stable/pango-Glyph-Storage.html#pango-glyph-string-index-to-x

where if my understanding is correct, we shouldn't PangoLayout which we currently do no, instead, we should first create a context from PangoCairo, pango-cairo-create-context, then use pango_itemize after that pango_shape or rather pango_shape_full, and then finally use pango_glyph_string_index_to_x for rendering a single single character with ligature on a cairo surface, while changing the colour in Cairo.

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Before doing this I would like to do #30

from manimpango.

This requires a major refactor so it can't be done now and is in the least priority because Manim's SVG parser still doesn't render Gradients from the SVG file.

from manimpango.