This demonstrates that the "imported" account behaves differently for a
wallet that's watch-only vs. normal. The testTaprootImportTapscriptFullKeyFundPsbt
test case succeeds in a normal run but fails in a remote-signing setup.
For some reason, an imported tapscript address ends up in the "default"
account when remote-signing but in the "imported" account for a normal
wallet.
With this commit we unify three existing PSBT channel funding
integration tests into a single one with the goal of testing all three
cases with simple taproot channels as well.