Type annotate Parameter.rx property

[MarcSkovMadsen]

VS Code and other editors relying on static typing does not understand what rx_expression below is because Parameter.rx property is not type annotated:

import param
class P(param.Parameterized):
    a = param.Number()
p = P(a=1)
rx_expression = p.param.a.rx()

This is a huge bummer on developer experience as you don't get any help from there.

Please type annotate it. It probably requires some reordering of the code to avoid circular imports.