Spyder: Add wheel for rtree to Mac installer

[ccordoba12]

We don't declare rtree as a dependency in our setup.py because it's a binary package and doesn't have wheels in PyPI.

So to add it to the Mac app we'd have either to find a Mac wheel for it (easy) or to compile it in Github Actions (hard).

@mrclary, could you take a look at this one?

[mrclary]

@ccordoba12, code snippets are working on macOS app. What exactly was rtree used for? Is there some behavior that I can look at?

[ccordoba12]

rtree allows us to paint a box around the snippet regions, so users can move between them using Tab. Could you test for that?

[mrclary]

@ccordoba12 @dalthviz, FYI I think that Toblerity/rtree#163 will have wheels uploaded to PyPi soon for windows, linux, and macOS.