PR 16866 renamed the 'decode' argument in gettransaction to 'verbose' to make it more consistent with other RPC calls like getrawtransaction.
However, it seems it inadvertently overloaded the 'details' fields when 'verbose' is passed. The result is that the original 'details' fields are no longer returned, which seems to be a breaking API change.
This PR takes the simplest path to restoring the 'details' fields by renaming them from 'details' back to 'decoded', while leaving the 'verbose' argument for API consistency.
It also addresses [this comment](https://github.com/bitcoin/bitcoin/pull/16185#discussion_r320740413) to mention that the 'decoded' field is identical to decoderawtransaction.
Update the RPC help, functional test, and release note.
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