qt: fix content getting exposed in header in `TableViewExt`

This is because clipping is not used here, so unfortunately if header is not inline and the view is interactive the content is exposed in the header.

We should use clipping here, for both viewport and event delivery (similar to play queue). Qt's ListView.OverlayHeader and ListView.PullBackHeader are practically useless, because unless the header/footer is placed outside the view, with these positioning we can not use clipping, and we need to handle the events manually in header and footer to not reach to the content.

I have put a note regarding this situation.

Regression since !7022 (merged).

Request review @chub.

modules/gui/qt/widgets/qml/TableViewExt.qml

@@ -112,7 +112,15 @@ FocusScope {
 
     property Component header: null
     property Item headerItem: view.headerItem?.loadedHeader ?? null
-    property color headerColor: "transparent"
+    // NOTE: Clipping is not used, so if header is not inline, it should have background to not expose the content.
+    // TODO: Investigate using clipping here, which makes more sense in general for views. Not using clipping
+    //       makes this view not suitable for using it in auxiliary places (non-main, which is not naturally
+    //       clipped by the window). In order to make use of clipping, the header should be placed outside of
+    //       the view (similar to play queue). This is already a requirement to prevent events reaching to
+    //       the delegate (such as, hovering over the header). As `clip: true` adjusts both the scene graph
+    //       viewport, and qt quick event delivery agent. Having a control as header and blocking the events
+    //       events reaching beneath is not a good behavior, as currently done here.
+    property color headerColor: (interactive && (headerPositioning !== ListView.InlineHeader)) ? colorContext.bg.primary : "transparent"
     property int headerTopPadding: 0