anki/python/pyqt

We handle PyQt specially for a few reasons:

• It ships with a few issues in its .pyi files that we want to correct.
• Bazel's Python tools install each package in a separate folder, but the various PyQt packages expect to be installed in the same location, and will give runtime linking issues when they are split up.

To update the version lock file, change to the folder with requirements.in, modify the file, and then run "bazel run //python:update". PyQt does not depend on platform-specific packages, so the update can be run on any platform.