Delay masking the last character in Password echo mode.

Delay masking the last character in Password echo mode.

If QT_GUI_PASSWORD_ECHO_DELAY is defined in qplatformdefs.h with an
integer value in milliseconds, QLineEdit and TextInput will display
the last character entered unmasked for that delay period and then
mask the character as normal.  If QT_GUI_PASSWORD_ECHO_DELAY is
not defined then the behaviour is unchanged.

Task-number: QTBUG-17003
Task-number: QTBUG-20719
(cherry picked from commit f9e7aee2019d321edd655bfde7de43f20a106971)

Change-Id: I9a8647a0adeb94fc6beea949cdce7336671c898e
Reviewed-by: Martin Jones <martin.jones@nokia.com>