Add a QDeadlineTimer overload for the waitFor* function on Q*Socket classes

And make the old integer-versions call the QDeadlineTimer versions.
The logic is simpler and using QDeadlineTimer in more places creates more consistency throughout Qt.

This includes QSslSocket::waitForEncrypted, QTcpSocket::waitForConnected, etc.
These APIs are not "best practice", but as long as we have them we should keep them updated.

Possibly do in multiple steps:
1. Rewrite internals to create and use a QDeadlineTimer
2. Add QDeadlineTimer overload
3. Make the int-version inline by way of the INLINE_SINCE machinery.