GH-3392 dirty initial MSA support that shares logic with Mojang flows

Both act as the first step of AuthContext.

launcher/minecraft/auth/flows/MojangLogin.cpp

@@ -0,0 +1,14 @@
+#include "MojangLogin.h"
+
+MojangLogin::MojangLogin(AccountData* data, QString password, QObject* parent) : AuthContext(data, parent), m_password(password) {}
+
+void MojangLogin::executeTask() {
+    m_requestsDone = 0;
+    m_xboxProfileSucceeded = false;
+    m_mcAuthSucceeded = false;
+
+    initMojang();
+
+    beginActivity(Katabasis::Activity::LoggingIn);
+    m_yggdrasil->login(m_password);
+}