[backport#16944][gui] send: include watch-only
[backport#16944][gui] send: include watch-only

Summary:
For wallets with WALLET_FLAG_DISABLE_PRIVATE_KEYS.

https://github.com/bitcoin/bitcoin/pull/16944/commits/848f88920853724511387ca0b7ef652fa14ced71

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Depends on D7293

Partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/16944 | PR16944]]

Test Plan:
  ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7294

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