[EGraph] equal_solve find the class because it can change du to a subst

Makefile

src/arith.ml

src/arith.mli

src/egraph_simple.ml

src/inputlang/altergo/popop_of_altergo.ml

src/inputlang/altergo/popop_of_altergo.mli

src/inputlang/altergo/symbols.ml

src/inputlang/altergo/symbols.mli

src/inputlang/altergo/ty.ml

src/inputlang/altergo/ty.mli

src/inputlang/altergo/why_lexer.mll

src/inputlang/altergo/why_parser.mly

src/inputlang/altergo/why_ptree.mli

src/inputlang/altergo/why_typing.ml

src/inputlang/altergo/why_typing.mli

src/uninterp.mli

src/util/exn_printer.ml

src/util/extmap.ml

src/util/loc.ml

src/util/strings.ml