Handle explicit color-related commands

[YishiMichael]

Proposed changes

• M manimlib/mobject/svg/mtex_mobject.py

Since MTex uses color for indexing submobjects, tex that originally brought with \color commands (or \textcolor, etc.) will cause failure. So I handled such a situation. Also, I reconstructed the algorithm in generate_tex() function, making svg files generated as few as possible.

Test

Code:

from manimlib import *


class Test(Scene):
    def construct(self):
        mtex = MTex(
            "{\\color{green} R G} {{Y}} B",
            tex_to_color_map={"R": RED},
            color=BLUE
        )
        mtex.set_color_by_tex("{{Y}}", YELLOW)
        self.add(mtex)

Result: