[Cashtab] Implement better tx functions on Send screen

Summary: Implement new transaction functions for Cashtab send screen

Test Plan:
npm test

Send a one-to-one tx with no msg https://explorer.e.cash/tx/a3be6995c3b3c73a8e8b614ed8fb9de150b65b0d06328a8dadd7bf92205eee55
Send a one-to-one tx with a msg https://explorer.e.cash/tx/3826a43eeb9d615d73d99679d88a3cc1fd5712ed02884c4b01b1815238af3e78
Send a one-to-many tx with no msg https://explorer.e.cash/tx/833fa20bb039d926166d63c48e6c7c52c8dff79723de57efe77aae82f18bc432
Send a one-to-many tx with msg https://explorer.e.cash/tx/be5c2a02454bd8e37b248c76dd50dfb533046ccee325ec927ac332e800ef2edb
Send an airdrop with no msg https://explorer.e.cash/tx/eba431d620c7004079bf9efd8a3a1a871a75d005fc208eab383642dae78ce719
Send an airdrop with a msg https://explorer.e.cash/tx/373407961ec5b8b9edc5d3a0f41ce6f01f89bfe14570d1bed8a26a7e673fbc2c

For all cases, fee should be ~2.01 sat per byte, and OP_RETURN should be at index 0 (if present)

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14938