refactor: add instance creation abstraction and move vanilla

This is so that 1. Code is more cleanly separated, and 2. Allows to more
easily add instance updating :)

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/minecraft/VanillaInstanceCreationTask.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "InstanceCreationTask.h"
+
+class VanillaCreationTask final : public InstanceCreationTask {
+    Q_OBJECT
+   public:
+    VanillaCreationTask(BaseVersionPtr version) : InstanceCreationTask(), m_version(version) {}
+    VanillaCreationTask(BaseVersionPtr version, QString loader, BaseVersionPtr loader_version);
+
+    bool createInstance() override;
+
+   private:
+    // Version to update to / create of the instance.
+    BaseVersionPtr m_version;
+
+    bool m_using_loader = false;
+    QString m_loader;
+    BaseVersionPtr m_loader_version;
+};