Fix Gtk3Backend button-press-event signal handler crash

The Gtk 3 docs say that the signal handler should take GdkEventButton
as a value, but in reality it seems that we have to take it as
a pointer. To reproduce the issue, double click any clickable view (e.g.
a TextField) in a Gtk3Backend app. The crash occurs because the
incorrect argument size causes the unmanaged SignalBox pointer to be
some random pointer. Why the crash didn't occur on non Rocky Linux
platforms still evades me.

Author: stackotter

Sources/Gtk3/Widgets/Widget.swift

@@ -24,13 +24,21 @@ open class Widget: GObject {
     }
 
     func didMoveToParent() {
+        // The Gtk3 docs claim that this handler should take GdkEventButton as a
+        // value, but that leads to crashes on Rocky Linux. These crashes are
+        // fixed by instead taking the event as a pointer. I've confirmed that
+        // this also leads to correct functionality on Rocky Linux (with correct
+        // mouse coordinates etc). The weird part is that this code works
+        // perfectly on macOS and Ubuntu with and without indirection. Huh??
+        // 
+        // The docs: https://docs.gtk.org/gtk3/signal.Widget.button-press-event.html
         let handler1:
             @convention(c) (
                 UnsafeMutableRawPointer,
-                GdkEventButton,
+                UnsafePointer<GdkEventButton>,
                 UnsafeMutableRawPointer
             ) -> Void = { _, value1, data in
-                SignalBox1<GdkEventButton>.run(data, value1)
+                SignalBox1<GdkEventButton>.run(data, value1.pointee)
             }
 
         addSignal(