lang: Add declare_program! macro

[acheroncrypto]

Problem

Adding dependencies in order to invoke CPIs or client interactions has a high chance of eventually resulting in a dependency hell.

anchor-gen was created in order to create a CPI client from IDLs without having to depend on the actual program crate, however, it has the following problems:

• Not compatible with the new IDL
• Only used for CPI
• Requires a separate crate for the external program

Solution

Add declare_program! macro to generate program declaration from the program's IDL:

declare_program!(program_name);

This creates a module named program_name with the following submodules:

• accounts: Program account type definitions
• client: Off-chain client helpers
• constants: Program constants
• cpi: On-chain CPI helpers
• events: Program event type definitions
• program: Program definition
• types: Program type definitions (excluding accounts and events)

This allows to interact with programs, both from on-chain and off-chain, without having to add the program's crate as a dependency.

Note that creating a separate crate (like with anchor-gen) is not required.

[vercel]

@acheroncrypto is attempting to deploy a commit to the coral-xyz Team on Vercel.

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