User documentation on import hook-based editable installs (PEP 660)

[debonte]

Add user documentation somewhere explaining:

• Why import hooks are a problem for static analysis tools
• The downside of opting out of import hooks -- your editable install may not match your real install as closely as it could.
• How to out-out of import hooks in common build backends. Graham started that here. We might need to move it for discoverability.
  • setuptools: legacy behavior / strict mode
  • hatchling
  • pdm

For https://github.com/microsoft/pyrx/issues/2715

[ofek]

Hatchling does the .pth file way by default

[debonte]

Hatchling does the .pth file way by default

Thanks @ofek. For hatchling I think we would just explain that dev-mode-exact = true enables import hooks and could cause issues with Pylance.