Non-Western fonts cannot align Western fonts and formulas

As the picture showed, Non-Western(Chinese, Japanese, for example) fonts cannot align Western fonts and formulas.


Here is the code:
```python
from manimlib import *
class Example(Scene):
def construct(self):
self.play(
Write(
MTexText("勾股定理 Pythagorean theorem のぬ $a^2+b^2=c^2$")
)
)
```

The issue demonstrates misalignment of mixed-language text in MTexText. Start by examining the manimlib/text/mtex.py file where MTexText is defined, and look at how text layout and font handling are implemented. Run the provided example to see the visual misalignment, then explore font metrics and alignment logic for combining Western and non-Western characters with LaTeX math.

由索引模型根据 Issue 内容生成。