Consistently use Cura.Menu and Cura.MenuItem

Some of these were using the built-in Menu and MenuItem, causing the menus to appear in different sizes.

Contributes to issue CURA-8688.

resources/qml/MainWindow/ApplicationMenu.qml

@@ -20,13 +20,12 @@ Item
     {
         id: applicationMenu
         width: parent.width
-        FileMenu {}
+        height: UM.Theme.getSize("context_menu").height
+        background: Item {}
 
+        FileMenu {}
         EditMenu {}
         ViewMenu {}
-
-        background: Rectangle {}
-
         SettingsMenu
         {
             //On MacOS, don't translate the "Settings" word.
@@ -38,13 +37,9 @@ Item
             //- https://doc.qt.io/qt-5/qmenubar.html#qmenubar-as-a-global-menu-bar
             title: (Qt.platform.os == "osx") ? "&Settings" : catalog.i18nc("@title:menu menubar:toplevel", "&Settings")
         }
-
         ExtensionMenu { id: extensionMenu }
-
         PreferencesMenu {}
-
         HelpMenu {}
-
     }
 
 

resources/qml/Menus/EditMenu.qml

@@ -7,7 +7,7 @@ import QtQuick.Controls 2.1
 import UM 1.6 as UM
 import Cura 1.0 as Cura
 
-Menu
+Cura.Menu
 {
     title: catalog.i18nc("@title:menu menubar:toplevel", "&Edit")
 

resources/qml/Menus/HelpMenu.qml

@@ -8,7 +8,7 @@ import UM 1.5 as UM
 import Cura 1.0 as Cura
 
 
-Menu
+Cura.Menu
 {
     id: helpMenu
     title: catalog.i18nc("@title:menu menubar:toplevel", "&Help")

resources/qml/Menus/MaterialMenu.qml

@@ -72,7 +72,7 @@ Cura.Menu
 
     Cura.MenuSeparator { visible: favoriteMaterialsModel.items.length > 0}
 
-    Menu
+    Cura.Menu
     {
         id: genericMenu
         title: catalog.i18nc("@label:category menu label", "Generic")
@@ -108,7 +108,7 @@ Cura.Menu
             Instantiator
             {
                 model: brandMaterials
-                delegate: Menu
+                delegate: Cura.Menu
                 {
                     id: brandMaterialsMenu
                     title: materialName

resources/qml/Menus/PreferencesMenu.qml

@@ -7,7 +7,7 @@ import QtQuick.Controls 2.4
 import UM 1.5 as UM
 import Cura 1.0 as Cura
 
-Menu
+Cura.Menu
 {
     id: preferencesMenu
 

resources/qml/Menus/PrinterTypeMenu.qml

@@ -7,7 +7,7 @@ import QtQuick.Controls 2.4
 import UM 1.5 as UM
 import Cura 1.0 as Cura
 
-Menu
+Cura.Menu
 {
     id: menu
     title: "Printer type"