[Feature Request] Support metal backend

[oraluben]

Possible relevant features

• jit support for metal (for both torch / mlx)
• dlpack ext support
• Example to build metal kernel with tvm-ffi

[tqchen]

tvm-ffi ABI is independent from device backend, so likely most of things needed are already here, we also try deliberately minimize device related logics to ensure this repo is minimal and stable. ABI wise, the function should already be able to interact with the Tensor with different devices(most other devices don't have official stream so there is no need to special case for them). Perhaps tvm is likely a better place some of the technical items(like jit metal, because there is no nvcc so need specific supports in compiler/runtime) for some more advanced metal runtime needs.