Fix implicit conversion warning

Marks the old functions as deprecated and adds new safe versions.The
new functions give access to the native descriptor safely. It also
fixes the original functions in Qt 6.

warning: implicit conversion loses integer precision: 'qintptr' (aka 'long long') to 'int'

Change-Id: I59177905af0181912d2e7824ce68265cb8ee03d9
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>