refactor(kernel/type_checker): remove "global" constraint buffer from type_checker, and use constraint_seq instead

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/unifier): missing set_conflict

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(library/standard): remove workarounds

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/unifier): allow computation when solving flex-rigid constraints

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