Expose `replace_tx`

[andreasgriffin]

Describe the enhancement

Expose TxBuilder::replace_tx (see bitcoindevkit/bdk#1799 ) in the ffi.

Use case

This is the only way to be able to "cancel" (RBF with different outputs) a transaction using the ffi.

[reez]

bitcoindevkit/bdk#1799 PR still open but will keep eyes on it

[thunderbiscuit]

Unfortunately the replace_tx method is not planned anymore, and focus moving forward will be on the new bdk-tx crate and the rewriting of the TxBuilder entirely.