Brace doesn't work with unicode-math

[xiao-ming-hub]

Describe the bug

When I use unicode-math package in tex_templates.yml and I use Brace to draw a curly brace, an error has occurred.

Code:

# custom_config.yml
tex:
  template: "basic"

# tex_templates.yml
# Line 8 and 9 are added
basic:
  description: ""
  compiler: latex
  preamble: |-
    \usepackage[english]{babel}
    \usepackage[mathrm=sym]{unicode-math}
    \setmathfont{Noto Sans Math}
    \usepackage{amsmath}
    \usepackage{amssymb}
    \usepackage{xcolor}

square = Square().set_fill(BLUE_E, 1)
# Here's where the error happens:
brace = Brace(square, UP)

Wrong display or Error traceback:

Traceback (most recent call last):
  ...
  File "/.../manimlib/scene/scene.py", line 155, in run
    self.construct()
    ~~~~~~~~~~~~~~^^
  File "/.../tmp.py", line 5, in construct
    brace = Brace(square, UP)
  File "/.../manimlib/mobject/svg/brace.py", line 50, in __init__
    self.set_initial_width(target_width)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/.../manimlib/mobject/svg/brace.py", line 58, in set_initial_width
    for tip, rect, vect in [(self[0], self[1], RIGHT), (self[5], self[4], LEFT)]:
                                      ~~~~^^^
  File "/.../manimlib/mobject/svg/string_mobject.py", line 551, in __getitem__
    return super().__getitem__(value)
           ~~~~~~~~~~~~~~~~~~~^^^^^^^
  File "/.../manimlib/mobject/mobject.py", line 405, in __getitem__
    return self.split().__getitem__(value)
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
IndexError: list index out of range

Additional context

The pack unicode-math is a convenient way to set the math font, but it also changes the way curly braces are rendered. LaTeX's original method was to use six characters to adjust the length by stretching, but in this package, the length is spliced according to the desired length, resulting in the subscript of self not corresponding.