Higher wallet-tx method combining RelayWalletTransactions and
AcceptToMemoryPool, using new Chain::broadcastTransaction
https://github.com/bitcoin/bitcoin/pull/15713/commits/611291c198eb2be9bf1aea1bf9b2187b18bdb3aau
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Partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/15713 | PR15713]]