Share "auto-detected" UI string and add tool tip

No need to have the same translatable string repeated at all these
places.
Also add tooltip to expand a bit on what "auto-detected" actually means.

Task-number: QTCREATORBUG-25291
Change-Id: I25d43486758ba17256cf7e1ea2eea0ec3d567b62
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/coreplugin/icore.h

@@ -101,6 +101,8 @@ public:
     static QString libexecPath();
     static QString crashReportsPath();
 
+    static QString ideDisplayName();
+
     static QString versionString();
 
     static QMainWindow *mainWindow();