rez-pip installation does not work for PySide6

[beatreichenbach]

Environment

• OS: Rocky Linux release 8.10 (Green Obsidian) x86_64
• Rez 3.2.1
• Python 3.11.11

To Reproduce
rez-pip --install --release --python-version 3.11 "PySide6"
Then load the package:
rez-env PySide6 -- python

>>> from PySide6 import QtWebEngineWidgets
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'QtWebEngineWidgets' from 'PySide6' 

The problem is PySide6 points to PySide6_Essentials instead of PySide6, meaning it can never fall back to PySide6_Addons.

I don't know exactly what went wrong during the installation with rez-pip but the packages that rez installed look different than the packages installed by normal pip in a virtual environment's site-packages directory.
For example, PySide6 in rez only contains stub files while PySide6 in the venv contains actual code.

[beatreichenbach]

The way to fix this is by copying the contents of

.../PySide6_Addons/python/PySide6
.../PySide6_Essentials/python/PySide6

into

.../PySide6/python/PySide6

and delete the other two directories, essentially removing those packages. This seems like some complicated setup that PySide is doing but since it is such a widely used package in our community, we might have to look into this.