feat(file-picker): add persistent ContentUrl functionality to pickFile on Android

[rbreckner]

Change reasons

I use the plugin in an app where usage of file picker and consumption of the returned path are not at the same moment. After restarting the app or rebooting the device, the path is invalidated on Android, while it works fine on iOS.

With the provided changes and my little understanding of native Android code, in pickFile(...) it is possible to optionally use a different Intent which grants persistence permission, which will be taken later inside the activity callback.

Pull request checklist

Please check if your PR fulfills the following requirements:

• The changes have been tested successfully.
• A changeset has been created (npm run changeset).

[robingenz]

Thank you for your PR. I am currently planning to make a complete rewrite of the plugin. For this reason I would like to leave your PR open. However, I keep this issue in mind.