Yet another osgpluginchecker rewrite

It turns out that it's possible for OSG plugins to be spread across multiple directories, and OSG doesn't account for this in osgDB::listAllAvailablePlugins(), even though it works when actually loading the plugin.

Instead, use code that's much more similar to how OSG actually loads plugin, and therefore less likely to miss anything.

Incidentally make things much simpler as we don't need  awkwardness from working around osgDB::listAllAvailablePlugins()'s limitations.

components/misc/osgpluginchecker.cpp.in

@@ -35,50 +35,14 @@ namespace Misc
 
     bool checkRequiredOSGPluginsArePresent()
     {
-        // work around osgDB::listAllAvailablePlugins() not working on some platforms due to a suspected OSG bug
-        std::filesystem::path pluginDirectoryName = std::string("osgPlugins-") + std::string(osgGetVersion());
-        osgDB::FilePathList& filepath = osgDB::getLibraryFilePathList();
-        for (const auto& path : filepath)
-        {
-#ifdef OSG_USE_UTF8_FILENAME
-            std::filesystem::path osgPath{ StringUtils::stringToU8String(path) };
-#else
-            std::filesystem::path osgPath{ path };
-#endif
-            if (!osgPath.has_filename())
-                osgPath = osgPath.parent_path();
-
-            if (osgPath.filename() == pluginDirectoryName)
-            {
-                osgPath = osgPath.parent_path();
-#ifdef OSG_USE_UTF8_FILENAME
-                std::string extraPath = StringUtils::u8StringToString(osgPath.u8string());
-#else
-                std::string extraPath = osgPath.string();
-#endif
-                filepath.emplace_back(std::move(extraPath));
-            }
-        }
-
-        auto availableOSGPlugins = osgDB::listAllAvailablePlugins();
+        // osgDB::listAllAvailablePlugins() lies, so don't use it
         bool haveAllPlugins = true;
         for (std::string_view plugin : USED_OSG_PLUGIN_NAMES)
         {
-            if (std::find_if(availableOSGPlugins.begin(), availableOSGPlugins.end(),
-                    [&](std::string_view availablePlugin) {
-#ifdef OSG_USE_UTF8_FILENAME
-                        std::filesystem::path pluginPath{ StringUtils::stringToU8String(availablePlugin) };
-#else
-                std::filesystem::path pluginPath {availablePlugin};
-#endif
-                        return pluginPath.filename()
-                            == std::filesystem::path(
-                                osgDB::Registry::instance()->createLibraryNameForExtension(std::string{ plugin }))
-                                   .filename();
-                    })
-                == availableOSGPlugins.end())
+            std::string libraryName = osgDB::Registry::instance()->createLibraryNameForExtension(std::string{ plugin });
+            if (osgDB::findLibraryFile(libraryName).empty())
             {
-                Log(Debug::Error) << "Missing OSG plugin: " << plugin;
+                Log(Debug::Error) << "Missing OSG plugin: " << libraryName;
                 haveAllPlugins = false;
             }
         }