add 'do-trace-shaders' setting and fix shaders recompiling

src/io/settings_io.cpp

@@ -89,6 +89,7 @@ SettingsHandler::SettingsHandler(EngineSettings& settings) {
     builder.section("debug");
     builder.add("generator-test-mode", &settings.debug.generatorTestMode);
     builder.add("do-write-lights", &settings.debug.doWriteLights);
+    builder.add("do-trace-shaders", &settings.debug.doTraceShaders);
     builder.add("enable-experimental", &settings.debug.enableExperimental);
 }