Add YML file of potentially unused methods
What does this MR do and why?
Add YML file of potentially unused methods
This allows us to more transparently track the methods we believe are
unused, which allows for more people to contribute to cleaning them up.
This also allows us to remove the hardcoded UNUSED_METHODS constant,
enabling us to generate better error messages with the eventual goal of
adding this script to our automated lefthook checks to help keep our
code from getting so crufty with unused methods in the first place.
Related to #420057
Screenshots
When we've stopped using a helper method
When we remove an unused helper method
Edited by Kerri Miller