Smart contract meta crate support

The library that provides all the functionality of the individual contracts meta crates.

The purpose of the contract meta crates is to produce the contract ABI. Because of their access to the ABI, they have other ABI-based responsibilities, such as:

• generating the wasm crates,
• building the contracts,
• performing validations not possible otherwise,
• generating snippets,
• etc.

For more about the build process, see https://docs.multiversx.com/developers/developer-reference/sc-build-reference/