Avoid deprecation warnings cased by GTK_ALIGN_BASELINE_FILL

We have to be careful to only use GDK_ALIGN_BASELINE_FILL when permitted
by GDK_VERSION_MAX_ALLOWED because gtkenums.h is a public header. If
it's not allowed, then just fall back to the previous definition of
GtkAlign since they are both compatible.

I don't think we can avoid conditional compilation here, because the old
definition is going to cause deprecated declaration warnings unless you
define an old GDK_VERSION_MIN_REQUIRED.

Fixes #5875

gtk/gtkenums.h

@@ -69,8 +69,13 @@ typedef enum
   GTK_ALIGN_START,
   GTK_ALIGN_END,
   GTK_ALIGN_CENTER,
+#if defined(GDK_VERSION_MAX_ALLOWED) && GDK_VERSION_MAX_ALLOWED < GDK_VERSION_4_12
+  GTK_ALIGN_BASELINE GDK_DEPRECATED_ENUMERATOR_IN_4_12_FOR(GTK_ALIGN_BASELINE_FILL),
+  GTK_ALIGN_BASELINE_FILL GDK_AVAILABLE_ENUMERATOR_IN_4_12 = GTK_ALIGN_BASELINE,
+#else
   GTK_ALIGN_BASELINE_FILL GDK_AVAILABLE_ENUMERATOR_IN_4_12,
   GTK_ALIGN_BASELINE GDK_DEPRECATED_ENUMERATOR_IN_4_12_FOR(GTK_ALIGN_BASELINE_FILL) = GTK_ALIGN_BASELINE_FILL,
+#endif
   GTK_ALIGN_BASELINE_CENTER GDK_AVAILABLE_ENUMERATOR_IN_4_12,
 } GtkAlign;