Avoid unnecessary copy in QByteArray::toDouble when created via fromRawData

Currently if we need to convert const char* to double in Qt, we must use QString::toDouble() or QByteArray::toDouble().

For example:

const char *text = "1234.56";

double d1 = QString::fromLatin1(text).toDouble();

double d2 = QByteArray::fromRawData(text, qstrlen(text)).toDouble()

But in both cases this results in unnecessary memory allocation.

I'm looking for some fast way to convert const char* to double, and I thought it would be nice if QLatin1String class have toDouble(), toLongLong(), etc. methods.

These methods could be used for example, in QPSQL driver to speed-up fetching large query results (100k+ rows) - for each double value in row we must do a conversion from const char* to double. There are standard C functions: atof(), atol(), but they use system locale, and can't be used in QPSQL.

Another solution would be to make the following functions available in public API:

qstrtod()
qstrntod()
qstrtoll()
qstrtoull()

from qtbase/src/corelib/tools/qlocale_tools_p.h