Add `wallet_suggestDraftTransaction` RPC method

[rekmarks]

"As a dapp developer, I would like to suggest a transaction to the user with some parameters specified, while allowing the user to edit the rest of them."

Alternatively, any / all transaction parameters are filled in by the dapp, but the transaction shows up in "edit mode" in the confirmation so that the user can modify some / all parameters.

We should do this via a new wallet_ RPC method, and @brad-decker suggested the name wallet_suggestDraftTransaction. Thanks to Twitter user person72443 for suggesting the feature.

[person-al]

Thanks so much for listening to my suggestion! I'm so excited for this. For a little extra context: my goal is to create a "tip jar" on my personal website. The current sendTransaction RPC is a little too complete for such a feature. I'd either have to build a transaction creation UI on my own or rely on the user to hit the edit button and go back. Instead, I would love to be able to open MetaMask at the beginning of the "create transaction" stage of things with the address pre-filled, but allow the user to decide exactly which token they're sending an how much.

Thanks again for listening! I'm quite excited for this and happy to help in any way I can.