Add GcalOverflowBin and GcalOverflowBinLayout

This is a bin that purposefully can let its child overflow the
allocation, based on the size request mode. This will be used
to allow the event widget to reach smaller widths.

src/gui/gcal-overflow-bin.h

@@ -0,0 +1,44 @@
+/* -*- mode: c; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/*
+ * gcal-overflow-bin-.h
+ * Copyright (C) 2022 Purism SPC
+ *
+ * gnome-calendar is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * gnome-calendar is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define GCAL_TYPE_OVERFLOW_BIN (gcal_overflow_bin_get_type ())
+
+G_DECLARE_DERIVABLE_TYPE (GcalOverflowBin, gcal_overflow_bin, GCAL, OVERFLOW_BIN, GtkWidget)
+
+struct _GcalOverflowBinClass
+{
+  GtkWidgetClass parent_class;
+};
+
+GtkWidget *gcal_overflow_bin_new (void) G_GNUC_WARN_UNUSED_RESULT;
+
+GtkWidget *gcal_overflow_bin_get_child (GcalOverflowBin *self);
+void       gcal_overflow_bin_set_child (GcalOverflowBin *self,
+                                        GtkWidget       *child);
+
+void gcal_overflow_bin_set_request_mode (GcalOverflowBin    *self,
+                                         GtkSizeRequestMode  request_mode);
+
+G_END_DECLS