q(v)snprintf(): mark the functions as \obsolete

We can't deprecate them, yet, because there are way too many users in
Qt and 6.8 is too close by now, but we should give users a heads-up
that better alternatives exist these days.

Pick-to: 6.7 6.5 6.2 5.15
Task-number: QTBUG-127110
Change-Id: Ic14e9d12fc746fdc65d6c0006756c37339aa25f0
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 3f54c71b78e4ed4ab513190bbcda89ae27256377)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/text/qvsnprintf.cpp

@@ -15,6 +15,10 @@ QT_BEGIN_NAMESPACE
 /*!
     \relates QByteArray
 
+    \obsolete
+
+    Use C++11's \c{std::vsnprintf()} from \c{<cstdio>} instead.
+
     A portable \c vsnprintf() function. Will call \c ::vsnprintf(), \c
     ::_vsnprintf(), or \c ::vsnprintf_s depending on the system, or
     fall back to an internal version.
@@ -67,6 +71,10 @@ int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
     \target bytearray-qsnprintf
     \relates QByteArray
 
+    \obsolete
+
+    Use C++11's \c{std::snprintf()} from \c{<cstdio>} instead.
+
     A portable snprintf() function, calls qvsnprintf.
 
     \a fmt is the \c printf() format string. The result is put into