Android: Make AndroidSdkManager::reloadPackages() non-blocking

The suggestion sounds simple, but when tracking the all usages ,and their usages, and their usages' usages, the thing looks really challenging.

In short: imagine you have a core function, used in many places, which is a bottleneck, and the only solution is to make in asynchronous. The consequence is to refactor all the usages together with their nested usages.

A current consequence: the blocking call, that freezes the main thread ~500ms, may come from many random code paths. All the code paths need to be analyzed and adapted to the async behavior.

WIP, marking many of usages: https://codereview.qt-project.org/c/qt-creator/qt-creator/+/598292