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

Both act as the first step of AuthContext.

launcher/minecraft/auth/flows/MSASilent.cpp

@@ -0,0 +1,16 @@
+#include "MSASilent.h"
+
+MSASilent::MSASilent(AccountData* data, QObject* parent) : AuthContext(data, parent) {}
+
+void MSASilent::executeTask() {
+    m_requestsDone = 0;
+    m_xboxProfileSucceeded = false;
+    m_mcAuthSucceeded = false;
+
+    initMSA();
+
+    beginActivity(Katabasis::Activity::Refreshing);
+    if(!m_oauth2->refresh()) {
+        finishActivity();
+    }
+}