Directly show feedback when pressing the slice button

CURA-6034

resources/qml/ActionPanel/SliceProcessWidget.qml

@@ -27,15 +27,21 @@ Column
 
     property real progress: UM.Backend.progress
     property int backendState: UM.Backend.state
+    // As the collection of settings to send to the engine might take some time, we have an extra value to indicate
+    // That the user pressed the button but it's still waiting for the backend to acknowledge that it got it.
+    property bool waitingForSliceToStart: false
+    onBackendStateChanged: waitingForSliceToStart = false
 
     function sliceOrStopSlicing()
     {
         if (widget.backendState == UM.Backend.NotStarted)
         {
+            widget.waitingForSliceToStart = true
             CuraApplication.backend.forceSlice()
         }
         else
         {
+            widget.waitingForSliceToStart = false
             CuraApplication.backend.stopSlicing()
         }
     }
@@ -94,9 +100,9 @@ Column
             anchors.right: parent.right
             anchors.left: parent.left
 
-            text: catalog.i18nc("@button", "Slice")
+            text: widget.waitingForSliceToStart ? catalog.i18nc("@button", "Processing"): catalog.i18nc("@button", "Slice")
             tooltip: catalog.i18nc("@label", "Start the slicing process")
-            enabled: widget.backendState != UM.Backend.Error
+            enabled: widget.backendState != UM.Backend.Error && !widget.waitingForSliceToStart
             visible: widget.backendState == UM.Backend.NotStarted || widget.backendState == UM.Backend.Error
             onClicked: sliceOrStopSlicing()
         }