Added BTC and Fiat amount on the confirmation screen for Lightning Invoice (#7425)

Added BTC and Fiat amount(as enabled by the user) on the confirmation screen for a Lightning Invoice in the Kivy GUI 

closes https://github.com/spesmilo/electrum/issues/7410

electrum/gui/kivy/main_window.py

@@ -973,6 +973,13 @@ class ElectrumWindow(App, Logger):
         #       via self.get_amount()... the need for converting back should be removed
         return format_satoshis_plain(x, decimal_point=self.decimal_point()) + ' ' + self.base_unit
 
+    def format_amount_and_units_with_fiat(self, x) -> str:
+        text = self.format_amount_and_units(x)
+        fiat = self.fx.format_amount_and_units(x) if self.fx else None
+        if text and fiat:
+            text += f' ({fiat})'
+        return text
+
     def format_fee_rate(self, fee_rate):
         # fee_rate is in sat/kB
         return format_fee_satoshis(fee_rate/1000) + ' sat/byte'

electrum/gui/kivy/uix/screens.py

@@ -341,7 +341,9 @@ class SendScreen(CScreen, Logger):
     def do_pay_invoice(self, invoice):
         if invoice.is_lightning():
             if self.app.wallet.lnworker:
-                self.app.protected(_('Pay lightning invoice?'), self._do_pay_lightning, (invoice,))
+                amount_sat = invoice.get_amount_sat()
+                msg = _("Pay lightning invoice?") + '\n\n' + _("This will send {}?").format(self.app.format_amount_and_units_with_fiat(amount_sat)) +'\n'
+                self.app.protected(msg, self._do_pay_lightning, (invoice,))
             else:
                 self.app.show_error(_("Lightning payments are not available for this wallet"))
         else: