feat(data/polynomial/erase_lead): add lemma erase_lead_card_support_eq (#5529)
feat(data/polynomial/erase_lead): add lemma erase_lead_card_support_eq (#5529)

One further lemma to increase the API of `erase_lead`.  I use it to simplify the proof of the Liouville PR.  In particular, it is used in a step of the proof that you can "clear denominators" when evaluating a polynomial with integer coefficients at a rational number.



leanprover-community/mathlib,leanprover-community/mathlib