pkgconfig files are installed into "site-packages/.*.mesonpy.libs/pkgconfig"

When the `meson.build` specifies a pkgconfig file, this file gets installed into a weird `.*.mesonpy.libs/pkgconfig` subdirectory of site-packages. This is e.g. happening with [dbus-python](https://pypi.org/project/dbus-python/).

```
$ find .venv | grep pc$
.venv/lib/python3.11/site-packages/.dbus_python.mesonpy.libs/pkgconfig/dbus-python.pc
```

Start with the meson.build pkgconfig installation used by dbus-python and reproduce the package layout in a Python 3.11 virtual environment. Trace where the .pc file is placed under site-packages and verify that the completed fix installs it in the expected location rather than under .mesonpy.libs/pkgconfig.

Written by the indexing model from the issue text.