Generate special signature ✨ composed of multiple elements instead of relying on timestamp for Java version cache invalidation

Signed-off-by: TheKodeToad <TheKodeToad@proton.me>

launcher/launch/steps/CheckJava.h

@@ -40,6 +40,6 @@ private:
 
 private:
     QString m_javaPath;
-    qlonglong m_javaUnixTime;
+    QString m_javaSignature;
     JavaCheckerPtr m_JavaChecker;
 };