Rename Workspace::restack() function

There are several ways how a window can be restacked relative to another:
either by placing it below the reference window or above the reference
window.

Currently, the restack() function places the given window below the
refererence window. But it's hard to decipher from the name, one needs
to take a look at the argument names to understand what's going on.

Another reason to rename is that it could be useful to have a stackAbove()
function to make X11Window::restackWindow() implementation simpler and
more straightforward.

src/layers.cpp

@@ -445,32 +445,32 @@ void Workspace::lowerWindowRequest(Window *window)
     lowerWindowWithinApplication(window);
 }
 
-void Workspace::restack(Window *window, Window *under, bool force)
+void Workspace::stackBelow(Window *window, Window *reference, bool force)
 {
     if (window->isDeleted()) {
-        qCWarning(KWIN_CORE) << "Workspace::restack: closed window" << window << "cannot be restacked";
+        qCWarning(KWIN_CORE) << "Workspace::stackBelow: closed window" << window << "cannot be restacked";
         return;
     }
-    if (!force && !Window::belongToSameApplication(under, window)) {
+    if (!force && !Window::belongToSameApplication(reference, window)) {
         // put in the stacking order below _all_ windows belonging to the active application
         for (int i = 0; i < unconstrained_stacking_order.size(); ++i) {
             auto other = unconstrained_stacking_order.at(i);
-            if (other->isClient() && other->layer() == window->layer() && Window::belongToSameApplication(under, other)) {
-                under = other;
+            if (other->isClient() && other->layer() == window->layer() && Window::belongToSameApplication(reference, other)) {
+                reference = other;
                 break;
             }
         }
     }
 
-    Q_ASSERT(unconstrained_stacking_order.contains(under));
-    if (under == window) {
+    Q_ASSERT(unconstrained_stacking_order.contains(reference));
+    if (reference == window) {
         return;
     }
 
     unconstrained_stacking_order.removeAll(window);
-    unconstrained_stacking_order.insert(unconstrained_stacking_order.indexOf(under), window);
+    unconstrained_stacking_order.insert(unconstrained_stacking_order.indexOf(reference), window);
 
-    m_focusChain->moveAfterWindow(window, under);
+    m_focusChain->moveAfterWindow(window, reference);
     updateStackingOrder();
 }
 
@@ -480,7 +480,7 @@ void Workspace::restackWindowUnderActive(Window *window)
         raiseWindow(window);
         return;
     }
-    restack(window, m_activeWindow);
+    stackBelow(window, m_activeWindow);
 }
 
 #if KWIN_BUILD_X11

src/tabbox/tabbox.cpp

@@ -226,7 +226,7 @@ void TabBoxHandlerImpl::raiseClient(Window *c) const
 
 void TabBoxHandlerImpl::restack(Window *c, Window *under)
 {
-    Workspace::self()->restack(c, under, true);
+    Workspace::self()->stackBelow(c, under, true);
 }
 
 void TabBoxHandlerImpl::elevateClient(Window *c, QWindow *tabbox, bool b) const

src/workspace.h

@@ -235,7 +235,7 @@ public:
 #endif
     void lowerWindowRequest(Window *window);
     void restackWindowUnderActive(Window *window);
-    void restack(Window *window, Window *under, bool force = false);
+    void stackBelow(Window *window, Window *reference, bool force = false);
     void raiseOrLowerWindow(Window *window);
     void updateStackingOrder(bool propagate_new_windows = false);
     void forceRestacking();

src/x11window.cpp

@@ -1738,7 +1738,7 @@ void X11Window::doSetShade(ShadeMode previousShadeMode)
         shade_geometry_change = false;
         if (previousShadeMode == ShadeHover) {
             if (shade_below && workspace()->stackingOrder().indexOf(shade_below) > -1) {
-                workspace()->restack(this, shade_below, true);
+                workspace()->stackBelow(this, shade_below, true);
             }
             if (isActive()) {
                 workspace()->activateNextWindow(this);
@@ -5503,7 +5503,7 @@ void X11Window::restackWindow(xcb_window_t above, int detail, NET::RequestSource
     }
 
     if (other) {
-        workspace()->restack(this, other);
+        workspace()->stackBelow(this, other);
     } else if (detail == XCB_STACK_MODE_BELOW) {
         workspace()->lowerWindowRequest(this, src, timestamp);
     } else if (detail == XCB_STACK_MODE_ABOVE) {