feat: add very early mod.toml packwiz support

Also use it as a on-disk format for storing mod metadata. This will be
used later on to make better mod managment.

launcher/minecraft/mod/LocalModUpdateTask.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <QDir>
+
+#include "tasks/Task.h"
+#include "modplatform/ModIndex.h"
+
+class LocalModUpdateTask : public Task {
+    Q_OBJECT
+   public:
+    using Ptr = shared_qobject_ptr<LocalModUpdateTask>;
+
+    explicit LocalModUpdateTask(QDir mods_dir, ModPlatform::IndexedPack& mod, ModPlatform::IndexedVersion& mod_version);
+
+    bool canAbort() const override { return true; }
+    bool abort() override;
+
+   protected slots:
+    //! Entry point for tasks.
+    void executeTask() override;
+
+   private:
+    QDir m_index_dir;
+    ModPlatform::IndexedPack& m_mod;
+    ModPlatform::IndexedVersion& m_mod_version;
+};