view: draw borders around actual dimensions

Previously if the view did not take the size requested, we would draw
the borders around the size we asked the view to take rather than its
actual size.

river/View.zig

@@ -264,6 +264,16 @@ pub fn getDefaultFloatBox(self: Self) Box {
     };
 }
 
+/// Return the dimensions of the actual "visible bounds" that the client has
+/// committed. This excludes any "invisible" areas of the surface that show
+/// useless stuff like CSD shadows.
+pub fn getActualBox(self: Self) Box {
+    return switch (self.impl) {
+        .xdg_toplevel => |xdg_toplevel| xdg_toplevel.getActualBox(),
+        .xwayland_view => |xwayland_view| xwayland_view.getActualBox(),
+    };
+}
+
 /// Called by the impl when the surface is ready to be displayed
 pub fn map(self: *Self) void {
     const root = self.output.root;