[OAuth] Investigate in-app browser tab support

The RFC 8252, which describes best practices for native applications (such as Qt applications), strongly
recommends on using the system browser to interact with the authorization server. This is for both usability and security reasons.
Notably it states that so-called embedded web views MUST NOT be used anymore.
This is due to security and usability reasons.

However there is a middle-ground known as in-app browser tab support. It's a mechanism to open a system browser tab without actually leaving the application. But since the tab is in fact the system browser, it has similar security characteristics. This requires support from the underlying operating system and browsers (Android and iOS both have support).

This task is a feasibility-analysis for adding Qt support for it.