Missing example and right docs on how to open photos from a library on the mobile device

If a user wants to learn how to open a photo from a library on a mobile device, he needs to make the following set of conclusions which requires a long experience of working with and in Qt:

• The widget API do not mention their use for this, It is not clear if this API can be used or not
• switch to Qt Quick
• need to know upfront that this would be via FileDialog in Qt Quick
• need to pay attention to the section "shortcuts : Object" which tells that "QStandardPaths" would give some "useful" paths, incl. QStandardPaths::PicturesLocation. BTW, it is not "useful", this is "essential"
• Go to QStandardPaths::PicturesLocation to see what "PicturesLocation" contains
• guess that this would be plausible to use ""assets-library://"" and not ""<APPROOT>/Documents/Pictures""
• get simple code to try if this works for this purpose

Not speaking of the fact that API can be much better or even this important use case deserves dedicated API, I wish:

• There will be a dedicated example for this use case for iOS and Android
• If Qt cannot handle the Photo Library on macOS
• Extend and correct the documentation so that it leads the user to the right API and right and clear parameters to be used