mathlib3

cbd88d63 - chore(*) add mod_add_div' and div_add_mod' and golf proofs (#5962)

chore(*) add mod_add_div' and div_add_mod' and golf proofs (#5962) Resolves issue #1534. Name of nat.mod_add_div shouldn't be changed as this is in core. Better name suggestions for mod_add_div' and div_add_mod' welcome. Co-authored-by: Julian <kuelsha@mathematik.uni-stuttgart.de>