Add a VisibilityParentWatcher utility (#156)

* Add a VisibilityParentWatcher utility

which forces visibilityChanged calls for you *or your parent*
visibility changing, optionally.

* Add a needed include

Author: baconpaul

include/sst/jucegui/util/VisibilityParentWatcher.h

@@ -0,0 +1,39 @@
+/*
+ * sst-jucegui - an open source library of juce widgets
+ * built by Surge Synth Team.
+ *
+ * Copyright 2023-2024, various authors, as described in the GitHub
+ * transaction log.
+ *
+ * sst-jucegui is released under the MIT license, as described
+ * by "LICENSE.md" in this repository. This means you may use this
+ * in commercial software if you are a JUCE Licensee. If you use JUCE
+ * in the open source / GPL3 context, your combined work must be
+ * released under GPL3.
+ *
+ * All source in sst-jucegui available at
+ * https://github.com/surge-synthesizer/sst-jucegui
+ */
+
+#ifndef INCLUDE_SST_JUCEGUI_UTIL_VISIBILITYPARENTWATCHER_H
+#define INCLUDE_SST_JUCEGUI_UTIL_VISIBILITYPARENTWATCHER_H
+
+#include <juce_gui_basics/juce_gui_basics.h>
+
+namespace sst::jucegui::util
+{
+/*
+ * If you create a member of this class, then you get
+ * visibilityChanged called *not* just when your visibility
+ * changes but when any of your parent hierarchy visibility
+ * changes
+ */
+struct VisibilityParentWatcher : juce::ComponentMovementWatcher
+{
+    VisibilityParentWatcher(juce::Component *that) : juce::ComponentMovementWatcher(that) {}
+    void componentMovedOrResized(bool wasMoved, bool wasResized) override {}
+    void componentPeerChanged() override {}
+    void componentVisibilityChanged() override { getComponent()->visibilityChanged(); }
+};
+} // namespace sst::jucegui::util
+#endif // VISIBILITYPARENTWATCHER_H