refactor(frontends/lean/elaborator): local context
refactor(frontends/lean/elaborator): local context

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

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