qml: implement RbF bump methods Decrease payment/Preserve payment

extend FormattedAmount to wrap alt to next line, or show as empty when invalid

electrum/gui/qml/components/controls/FormattedAmount.qml

@@ -5,20 +5,38 @@ import QtQuick.Controls.Material 2.0
 
 import org.electrum 1.0
 
-RowLayout {
+GridLayout {
     required property Amount amount
     property bool showAlt: true
+    property bool singleLine: true
+    property bool valid: true
+
+    columns: !valid
+                ? 1
+                : singleLine
+                    ? 3
+                    : 2
+
+    Item {
+        visible: !valid // empty placeholder if not valid
+        Layout.preferredWidth: 1
+        Layout.preferredHeight: 1
+    }
     Label {
+        visible: valid
         text: amount.msatsInt > 0 ? Config.formatMilliSats(amount) : Config.formatSats(amount)
         font.family: FixedFont
     }
     Label {
+        visible: valid
         text: Config.baseUnit
         color: Material.accentColor
     }
 
     Label {
-        visible: showAlt && Daemon.fx.enabled
+        Layout.columnSpan: singleLine ? 1 : 2
+        visible: showAlt && Daemon.fx.enabled && valid
         text: '(' + Daemon.fx.fiatValue(amount) + ' ' + Daemon.fx.fiatCurrency + ')'
+        font.pixelSize: constants.fontSizeSmall
     }
 }