This is an opt-in trade-off between type safety and user
code convenience.

QT_NO_CAST_FROM_ASCII is highly beneficial to avoid unintended
conversions from 8 bit data with potentially "unsuitable"
encodings to QString. However, it has the undesirable side-effect
to require user code to wrap character and string literals
in QLatin1Char(...) and QLatin1String(...) or use similar
construction, cluttering the code significantly.

QT_RESTRICTED_CAST_FROM_ASCII macro works almost as
QT_NO_CAST_FROM_ASCII, except that it enables the QChar(char)
constructor and adds an additional QString(const char (&ch)[N])
constructor that matches C++ string literals, but no arbitrary
character pointers.

This avoids a significant share of the need to clutter the
user code by only a slight relaxation of the type-safety.

Change-Id: I64e0430bb1352edcedf7e19ee25c16408727084c
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>