Support KeyChain for text field

It'd be nice to have support for iCloud/Android KeyChain so it can store and auto-fill login username and passwords, and allow fingerprint login. The use case is that you would have an app which has a login with a username and password. Qt various possibilities handle sensitive data, like Qt::ImhSensitiveData and QLineEdit::Password but apparently, there are no API where the user can define that a field should be marked as one which can be handled by the platform as storable in a KeyChain or another system on a platform.  

Here is the reference form the Apple developer docs: https://developer.apple.com/documentation/security/password_autofill/enabling_password_autofill_on_a_text_input_view?language=objc

Here is a summary of an internal chat on this FYI:

• Qt does not any user API for specifying the related input item type, nor on the input method level
• same issue will exist basically on Android and WASM 
• Desktop platforms have (for the most part) no auto-completion API
• A the building block at the QPA layer would be required