[OSS] Light Validation

[h4x3rotab]

light_validation module implements a Substrate light client. Currently it's coupled with our TEE and blockchain implementation. However to make it easier to share with other projects, we should make it a separate crate.

Caveats

1. The code is coupled with Phala's blockchain because it uses the types defined in our blockchain runtime. We should remove it and only rely on Substrate itself.
2. We have a hack to walk around the Substrate's no_std environment. The problem is that Substrate treats no_std environment as wasm, where Substrate exposes the external hash function as a host function, but it's not the case in TEE. So now we require the runtime to use the above repo as a mitigation. We need to document it somewhere, or find a better way to fix it.

Progress

• Fully functional light client
• Extract as a standalone package
• Parachain client demo
• Tests & lint
• Documentation