Native linux VST support (#6048)

Co-authored-by: Dominic Clark <mrdomclark@gmail.com>

src/core/DataFile.cpp

@@ -213,6 +213,9 @@ bool DataFile::validate( QString extension )
 				( extension == "xiz" && ! getPluginFactory()->pluginSupportingExtension(extension).isNull()) ||
 				extension == "sf2" || extension == "sf3" || extension == "pat" || extension == "mid" ||
 				extension == "dll"
+#ifdef LMMS_BUILD_LINUX
+				|| extension == "so"
+#endif
 #ifdef LMMS_HAVE_LV2
 				|| extension == "lv2"
 #endif

src/gui/FileBrowser.cpp

@@ -1248,7 +1248,11 @@ void FileItem::determineFileType( void )
 		m_type = MidiFile;
 		m_handling = ImportAsProject;
 	}
-	else if( ext == "dll" )
+	else if( ext == "dll"
+#ifdef LMMS_BUILD_LINUX
+		|| ext == "so" 
+#endif
+	)
 	{
 		m_type = VstPluginFile;
 		m_handling = LoadByPlugin;