feat(kernel/type_checker): use expression before normalization in the unification constraints generated by the typechecker
feat(kernel/type_checker): use expression before normalization in the unification constraints generated by the typechecker

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

leanprover/lean,fpvandoorn/lean2,levnach/lean,sp3ctum/lean,Kha/lean,dselsam/lean,leodemoura/lean,soonhokong/travis_test,codyroux/lean0.1,leanprover-community/lean,c-cube/lean,avigad/lean,UlrikBuchholtz/lean,dselsam/lean,codyroux/lean0.1,fpvandoorn/lean,c-cube/lean,fpvandoorn/lean2,soonhokong/lean-osx,soonhokong/travis_test,javra/lean,fpvandoorn/lean,javra/lean,htzh/lean,soonhokong/lean-osx,rlewis1988/lean,soonhokong/lean,johoelzl/lean,soonhokong/lean-osx,fpvandoorn/lean2,johoelzl/lean,levnach/lean,eigengrau/lean,leanprover/lean,fpvandoorn/lean,digama0/lean,leanprover/lean,fgdorais/lean,soonhokong/lean-osx,eigengrau/lean,sp3ctum/lean,johoelzl/lean,fgdorais/lean,UlrikBuchholtz/lean,sp3ctum/lean,eigengrau/lean,UlrikBuchholtz/lean,dselsam/lean,rlewis1988/lean,levnach/lean,rlewis1988/lean,soonhokong/lean,Kha/lean,johoelzl/lean,Kha/lean,soonhokong/lean-windows,soonhokong/travis_test,dselsam/lean,avigad/lean,avigad/lean,avigad/lean,fgdorais/lean,rlewis1988/lean,htzh/lean,c-cube/lean,rlewis1988/lean,soonhokong/travis_test,sp3ctum/lean,fpvandoorn/lean2,soonhokong/lean-windows,fpvandoorn/lean,leanprover-community/lean,leodemoura/lean,eigengrau/lean,soonhokong/lean-windows,javra/lean,levnach/lean,digama0/lean,javra/lean,soonhokong/lean,htzh/lean,digama0/lean,fpvandoorn/lean,soonhokong/lean-windows,leanprover/lean,fpvandoorn/lean,fgdorais/lean,leodemoura/lean,Kha/lean,dselsam/lean,soonhokong/lean-osx,soonhokong/lean,leanprover-community/lean,fgdorais/lean,dselsam/lean,htzh/lean,leodemoura/lean,leodemoura/lean,fpvandoorn/lean2,johoelzl/lean,digama0/lean,leanprover-community/lean,Kha/lean,digama0/lean,c-cube/lean,javra/lean,fgdorais/lean,leanprover/lean,htzh/lean,codyroux/lean0.1,rlewis1988/lean,leodemoura/lean,UlrikBuchholtz/lean,soonhokong/lean-windows,leanprover-community/lean,digama0/lean,Kha/lean,leanprover/lean,eigengrau/lean,soonhokong/lean,codyroux/lean0.1,avigad/lean,levnach/lean,sp3ctum/lean,c-cube/lean,UlrikBuchholtz/lean,leanprover-community/lean,avigad/lean,johoelzl/lean