Prototyping canonical SolanaTBTC token with Anchor

[eth-r]

Refs: #656

This PR is a continuation of tBTC expansion to L2s, sidechains, and non-EVM chains - here Solana. Solana module in large should replicate the same functionality as available in other cross-chain modules like Arbitrum, Optimism, and Polygon. It brings tBTC to Solana with the help of Wormhole. Here's a diagram to illustrate the flow

+----------------------------+         +----------------------------------------------------------------------+
|          Ethereum          |         |                                Solana                                |
|                            |         |                                                                      |
|  +----------------------+  |         |  +----------------------+  +-----------------------+  +------------+ |
|  | Wormhole TokenBridge |--|---------|--| Wormhole TokenBridge |--| SolanaWormholeGateway |--| SolanaTBTC | |
|  +----------------------+  |         |  +----------------------+  +-----------------------+  +------------+ |
|                            |         |                                                                      |
+----------------------------+         +----------------------------------------------------------------------+

Wormhole TokenBridge on Ethereum - holds all TBTC bridged to Solana. This is an external contract created by the Wormhole team.
Wormhole TokenBridge on Solana - mints Wormhole wrapped TBTC ie. wormholeTBTC. This is an external contract created by the Wormhole team.
SolanaWormholeGateway on Solana - acts as a vending machine that wraps and unwraps wormholeTBTC to the canonical tBTC token on Solana. (TO BE YET IMPLEMENTED by the Threshold team)
SolanaTBTC - canonical tBTC token on Solana. This PR creates it and sets up the project structure.

---

Links:

• generic implementation of the Canonical TBTC written in Solidity
• generic implementation of the Wormhole Gateway written in Solidity:

[dimpar]

Do you think we can change the project structure like:

cross-chain
|-solana
  |-programs
    |-tbtc
      |-src
        |-lib.rs
      |-Cargo.toml
      |-Xargo.toml
    |-wormhole-gateway (to be added)
      |-src
        |-lib.rs
      |-Cargo.toml
      |-Xargo.toml
  |-migrations
  |-tests
  (rest of the files)

[a5-pickle]

Minor issue, but this authority should be the same pubkey as the one who deployed the program. The upgrade authority (found in this program's program data, which is an account owned by BpfLoaderUpgradeable) will be this authority. Unlikely, but someone can race you to initialize the instruction after you deploy, setting himself as the authority.

Also a note about upgradeability: how do you plan on managing this? Multisig? You should set the upgrade authority to your multisig address in this instruction. Or it can be managed by an external program, where that external program's PDA can be the upgrade authority.

[dimpar]

After the deployment on mainnet we want to set the upgrade authority as Threshold Council multisig.

[a5-pickle]

Left some comments.

I also did not see any CPI with the token bridge yet, but I assume this is a work-in-progress. I can take a look again once these CPI calls are written.

[a5-pickle]

NOTE: Wormhole Gateway is still a work-in-progress. Everything looks good so far.

[eth-r]

Can't approve this myself, but looks good to me.