feat: basic plugin system

The wayland plugin now uses it.

src/core/plugin.cpp

@@ -0,0 +1,35 @@
+#include "plugin.hpp"
+#include <algorithm>
+
+#include <qvector.h> // NOLINT (what??)
+
+// defined by moc. see below comment.
+void qml_register_types_QuickShell(); // NOLINT
+
+static QVector<QuickshellPlugin*> plugins; // NOLINT
+
+void QuickshellPlugin::registerPlugin(QuickshellPlugin& plugin) { plugins.push_back(&plugin); }
+
+void QuickshellPlugin::initPlugins() {
+	plugins.erase(
+	    std::remove_if(
+	        plugins.begin(),
+	        plugins.end(),
+	        [](QuickshellPlugin* plugin) { return !plugin->applies(); }
+	    ),
+	    plugins.end()
+	);
+
+	for (QuickshellPlugin* plugin: plugins) {
+		plugin->init();
+	}
+
+	// This seems incredibly stupid but it appears qt will not register the module types
+	// if types are already defined for the module, meaning qmlRegisterType does not work
+	// unless the module types are already registered.
+	qml_register_types_QuickShell();
+
+	for (QuickshellPlugin* plugin: plugins) {
+		plugin->registerTypes();
+	}
+}