QByteArray: optimize replace() a bit

These days, we perform the alias check unconditionally, so the remainder of the function can assume that *this and after do not overlap. So memcpy() suffices, we don't need memmove().

Pick-to: 6.3 6.2
Change-Id: Ib6966facfe643b0aaf50d902709f5fe926bed527
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/text/qbytearray.cpp

@@ -2170,7 +2170,7 @@ QByteArray &QByteArray::replace(qsizetype pos, qsizetype len, QByteArrayView aft
     }
     if (len == after.size() && (pos + len <= size())) {
         detach();
-        memmove(d.data() + pos, after.data(), len*sizeof(char));
+        memcpy(d.data() + pos, after.data(), len*sizeof(char));
         return *this;
     } else {
         // ### optimize me