Force destruction of webcontent client before profile adapter

Currently users might forget to delete webcontent client before
profile adapter. This might be nasty if users are not aware of default
profile. Instead of asserting badly in chromium, clean up and release
chromium resources.

This avoids the crash, but might leak memory if users never deletes
page.

Task-number: QTBUG-74021
Change-Id: I66f466f169d12f7ee08866d505260dca47800bb0
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>