Incompatibility between pydrake and Mypy

[jwnimmer-tri]

See #16987 for some background.

In our pydrake releases, we install *.pyi files so that people who use VSCode will have auto-complete enabled.

However, our *.pyi files are currently malformed in several ways, which means that if someone tries to run mypy type checking with pydrake in the loop, it will error out with syntax errors.

The work-around for the moment is to delete the *.pyi files if you intent to use mypy.

(Details to follow.)

[jwnimmer-tri]

Here's a tip from a user who found another work-around: if you move the *.pyi files out of your venv and into a typings directory, apparently VSCode will still find them there, but it won't confuse Mypy.