fix RTL appearance for ComboBox

Summary:
-- when the combobox isnt inside the main Item
but rather a sub-Item it doesnt inherit the
LayoutMirroring properties. This is a workaround
to handle that behavior.
QTBUG: https://bugreports.qt.io/browse/QTBUG-66446

Test Plan:
checkout that LayoutMirroring works properly in
such case

Reviewers: #plasma, mart, safaalfulaij

Reviewed By: safaalfulaij

Subscribers: safaalfulaij, plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D10592

src/declarativeimports/plasmacomponents3/ComboBox.qml

@@ -110,7 +110,11 @@ T.ComboBox {
             currentIndex: control.highlightedIndex
             highlightRangeMode: ListView.ApplyRange
             highlightMoveDuration: 0
-            LayoutMirroring.enabled: true
+            // HACK: When the ComboBox is not inside a top-level Window, it's Popup does not inherit
+            // the LayoutMirroring options. This is a workaround to fix this by enforcing
+            // the LayoutMirroring options properly.
+            // QTBUG: https://bugreports.qt.io/browse/QTBUG-66446
+            LayoutMirroring.enabled: Qt.application.layoutDirection === Qt.RightToLeft
             LayoutMirroring.childrenInherit: true
             T.ScrollBar.vertical: Controls.ScrollBar { }
         }