Merge bitcoin-core/gui#441: Add Create Unsigned button to SendConfirmationDialog

742918c8ef qt: hide Create Unsigned button behind an expert mode option (Andrew Chow)
5c3b800acd qt: Add Create Unsigned button to SendConfirmationDialog (Andrew Chow)

Pull request description:

  Instead of having different buttons or changing button behavior for making a PSBT, just have SendConfirmationDialog return whether the user wants a PSBT or a broadcasted transaction. Since this dialog is used by both the bumpFeeAction and the SendCoinsDialog, changes to both to support the different behavior is needed. They will check the return value of the SendConfirmationDialog for whether a PSBT needs to be created instead of checking whether private keys are disabled.

  Strings used in this dialog are being slightly modified to work with both private keys enabled and disabled wallets.

  Moved from https://github.com/bitcoin/bitcoin/pull/18789

ACKs for top commit:
  jarolrod:
    ACK 742918c
  ryanofsky:
    Code review ACK 742918c8ef. Just suggested changes since last review. Looks great!
  hebasto:
    ACK 742918c8ef, tested on Linux Mint 20.2 (Qt 5.12.8).

Tree-SHA512: dd29f4364c7b4f15befe8fe63257b26187918786b005e0f8336183270b1a162680b93f6ced60f0285c6e607c084cc0d24950fc68a8f9c056521ede614041be66

src/qt/forms/optionsdialog.ui

@@ -252,6 +252,16 @@
             </property>
            </widget>
           </item>
+          <item>
+           <widget class="QCheckBox" name="m_enable_psbt_controls">
+            <property name="text">
+             <string extracomment="An options window setting to enable PSBT controls.">Enable &amp;PSBT controls</string>
+            </property>
+            <property name="toolTip">
+             <string extracomment="Tooltip text for options window setting that enables PSBT controls.">Whether to show PSBT controls.</string>
+            </property>
+           </widget>
+          </item>
          </layout>
         </widget>
        </item>