[Cashtab] [BCH deprecation] [TxBuilder] Pt 2/8 - Deprecate BCH.TransactionBuilder in sendXec

Summary:
T2730

Depends on D12541

This diff deprecates the use of BCH-JS' transaction builder and replaces it with the local implementation for the sendXec function.

Pt 1/8 - Localize Transaction Builder module
Pt 2/8 - Deprecate BCH.TransactionBuilder in sendXec
Pt 3/8 - Add local TxBuilder to createToken
Pt 4/8 - Deprecate BCH.TransactionBuilder in createToken
Pt 5/8 - Add local TxBuilder to sendToken
Pt 6/8 - Deprecate BCH.TransactionBuilder in sendToken
Pt 7/8 - Add local TxBuilder to burnToken
Pt 8/8 - Deprecate BCH.TransactionBuilder in burnToken

Test Plan:

• npm ci
• npm test and ensure no errors with txBuilder.test.js
• npm start
• test the following transactions and verify in wallet and explorer:
• one to one XEC tx
• one to one XEC tx with an unencrypted message
• one to one XEC tx with an encrypted message
• one to many XEC tx
• one to many XEC tx with an unencrypted message
• airdrop one to many XEC tx
• airdrop one to many XEC tx with an unencrypted message

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12553