[RELAY] Refactor type inference to use type solver (#1779)

.gitignore

include/tvm/relay/op.h

include/tvm/relay/pass.h

include/tvm/relay/type.h

include/tvm/runtime/packed_func.h

python/tvm/relay/expr.py

python/tvm/relay/ty.py

src/common/arena.h

src/relay/ir/environment.cc

src/relay/ir/type.cc

src/relay/op/type_relations.cc

src/relay/op/type_relations.h

src/relay/pass/incomplete_type.h

src/relay/pass/resolve.cc

src/relay/pass/resolve.h

src/relay/pass/type_functor.h

src/relay/pass/type_infer.cc

src/relay/pass/type_solver.cc

src/relay/pass/type_solver.h

src/relay/pass/type_visitor.h