libobs: Add task scheduling features

(This commit also modifies the UI)

Adds the ability to schedule tasks for certain threads

UI/obs-app.cpp

@@ -1327,6 +1327,17 @@ void OBSApp::Exec(VoidFunc func)
 	func();
 }
 
+static void ui_task_handler(obs_task_t task, void *param, bool wait)
+{
+	auto doTask = [=]() {
+		/* to get clang-format to behave */
+		task(param);
+	};
+	QMetaObject::invokeMethod(App(), "Exec",
+				  wait ? WaitConnection() : Qt::AutoConnection,
+				  Q_ARG(VoidFunc, doTask));
+}
+
 bool OBSApp::OBSInit()
 {
 	ProfileScope("OBSApp::OBSInit");
@@ -1338,6 +1349,8 @@ bool OBSApp::OBSInit()
 	if (!StartupOBS(locale.c_str(), GetProfilerNameStore()))
 		return false;
 
+	obs_set_ui_task_handler(ui_task_handler);
+
 #ifdef _WIN32
 	bool browserHWAccel =
 		config_get_bool(globalConfig, "General", "BrowserHWAccel");