feat: Move the Python bindings into a standalone repository

[DataTriny]

Just like we did for the C bindings, let's move the Python ones into their own.

I used git-filter-repo to only keep what is relevant here.

GitHub secret tokens that we need to configure:

• RELEASE_PLEASE_TOKEN
• PYPI_TOKEN

[mwcampbell]

I believe you need to update the release-please workflow as I did for accesskit-c.

[DataTriny]

I performed a test of the release process here. The uploaded package can be found here.

On Pypi, in the project publishing settings, you will need to change the repository name to accesskit-python and the workflow file to publish.yml otherwise the upload will be rejected.