Split IronPython package into separate repository

[glopesdev]

This was originally planned for the 2.8 release, but we decided to give it a few more iterations to solve and test remaining issues with dependencies and backwards compatibility of the now obsolete Bonsai.Scripting bridge package.

Since there is now a stable migration path, the branching off plan should be resumed to move the code and documentation into bonsai-rx/ironpython-scripting, and both the IronPython and the legacy scripting bridge package should be removed from this repository.