feat(analysis/special_functions/integrals): integral of `|x - a| ^ n` over `Ι a b` (#9752)
feat(analysis/special_functions/integrals): integral of `|x - a| ^ n` over `Ι a b` (#9752)

Also use notation for `interval a b` and `interval_oc a b`.





leanprover-community/mathlib,leanprover-community/mathlib