QRegularExpression: add optimizations autotest

QRegularExpression: add optimizations autotest

Exporting the counter that controls the optimization of a compiled
pattern lets us to forcibly optimize all patterns. Therefore,
two tests are now run: one with default optimization values
and another one which always optimizes the pattern.

The counter itself was renamed with a qt_ prefix and put
inside the Qt compilation namespace
(thanks to rohanpm for pointing it out).

Change-Id: I56602433d37adc127772b2d0d2cdaf2e49d43c71
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>