Look into way to mass rewrite add parameter

[jenshnielsen]

Once #4412 lands it would be nice to transform all call of the form

self.add_parameter(name="foo", ...)

to

self.foo = self._add_parameter(name="foo" ....)
"""
Parameter foo
"""

So that parameters are documented, and completion works as expected.

Investigate how much effort it would take to do this using ast or similar.
See https://stackoverflow.com/questions/36022935/rewriting-code-with-ast-python for inspiration