Better support for perpetual (commercial) licenses for older Qt versions

Scenario

The offline installer cannot add components to an existing installation; only the online installer supports this. However, the online installer doesn't let the user install the commercial version of Qt if the user has a perpetual license that doesn't cover the latest version of Qt.

Furthermore, https://account.qt.io/downloads does not allow commercial users to download older versions of the Online installer.

Reports

• https://forum.qt.io/topic/91751/offline-installer-enterprise-edition-miss-add-components-feature
• https://forum.qt.io/topic/96412/online-installer-does-not-allow-to-install-commercial-licenced-version-of-qt

Workarounds

To add a new compoent, the holder of an old perpetual license must uninstall everything and re-install using the offline installer.

Suggestions

1. The offline installer should support adding components. AND/OR
2. The online installer should allow the holder of an old perpetual license to install the version(s) of Qt covered by the license.