Bad kerning in `Text()`

## Description of bug / unexpected behavior

When using `Text()` or `Paragraph()`, the spacing between letters is generally off regardless of the choice of the font. This is probably an issue with Pango.

See the attached images.

## Expected behavior

The spacing between the letters should be more balanced and evenly distributed.

## How to reproduce the issue

Code for reproducing the problem

```py
class DemoScene(Scene):
def construct(self):
paragraph = Paragraph(
"""
Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore
magna aliqua. Ut enim ad minim veniam, quis nostrud.""",
font="Helvetica", font_size=32, line_spacing = 0.5
)
self.add(paragraph)
```

## Additional media files

Images/GIFs


## Logs
Terminal output

```
PASTE HERE OR PROVIDE LINK TO https://pastebin.com/ OR SIMILAR
```

## System specifications

System Details

I rendered it using the Manimator in the Manim Community Server. The version is 0.15.2

- OS (with version, e.g., Windows 10 v2004 or macOS 10.15 (Catalina)):
- RAM:
- Python version (`python/py/python3 --version`):
- Installed modules (provide output from `pip list`):
```
PASTE HERE
```

LaTeX details

+ LaTeX distribution (e.g. TeX Live 2020):
+ Installed LaTeX packages:

FFMPEG

Output of `ffmpeg -version`:

```
PASTE HERE
```

## Additional comments

Start by reproducing the supplied DemoScene using Text() or Paragraph() with the shown font and line spacing, then compare the rendered letter spacing across fonts. Investigate the text-rendering path and the suspected Pango interaction. Done means the reproduced output has balanced, consistent spacing without regressing other text rendering.

Written by the indexing model from the issue text.