Allow prove_eq_by_Proper to prove Proper instances recursively and by assumption (#135)

For mit-plv/fiat-crypto#1778

Author: JasonGross

src/Rewriter/Rewriter/ProofsCommonTactics.v

@@ -490,8 +490,10 @@ Module Compilers.
              [ now
                  let H := fresh in
                  cbv [Proper respectful] in *;
-                 intro H; eapply H; intros; subst; eauto
+                 intro H; eapply H; intros; subst; eauto;
+                 prove_eq_by_Proper
              | first [ now typeclasses eauto
+                     | now cbv [Proper respectful] in *; typeclasses eauto with core
                      | idtac "WARNING: Could not find Proper instance";
                        clear;
                        print_context_and_goal ();