Improve SVG path parsing by using the referenced path

[mjmjmtl]

Motivation

In SVG file, a reference path is created for same characters:

When parsing the path in SVGMobject, parsing the reference path is better because:

1. It only stores one copy of path (for same character) in PATH_TO_POINTS cache.
2. The numerical accuracy is slightly better when doing the transform by ourselves.

Proposed changes

Here's the code to test the change:

from manimlib import *
from manimlib.mobject.svg.svg_mobject import PATH_TO_POINTS


class SVGTransformShowcase(Scene):
    def construct(self):
        tex = Tex("aaaaa")
        tex.scale(3)
        self.add(tex)
        print(f"{len(PATH_TO_POINTS)=}")

before:

after:

Notice the difference in terminal output.