[RF] Consistent minimizer defaults in RooAbsPdf::fitTo()

Take the default offsetting flag value from the default
`MinimizerConfig` struct, where the offsetting flag is correctly
initialized to `int doOffset = -1`:
https://github.com/root-project/root/blob/master/roofit/roofitcore/src/FitHelpers.cxx#L247

This means to not change any offset setting by default.

The problem was that the default was set to zero before, which tells the
minimizer to explicitly disable offsetting, even if the likelihood was
created with offsetting.

This fixes an issue reported on the forum:
https://root-forum.cern.ch/t/cannot-use-offset-with-rooabspdf-fitto/64293

Also, make sure that all other default config values are taken from the
default options struct for consistency.

To be backported to the previous active ROOT releases.

Author: guitargeek

roofit/roofitcore/src/FitHelpers.cxx

@@ -246,7 +246,7 @@ struct MinimizerConfig {
    int maxCalls = -1;
    int doOffset = -1;
    int parallelize = 0;
-   bool enableParallelGradient = true;
+   bool enableParallelGradient = false;
    bool enableParallelDescent = false;
    bool timingAnalysis = false;
    const RooArgSet *minosSet = nullptr;
@@ -420,8 +420,7 @@ std::unique_ptr<RooAbsReal> createNLLNew(RooAbsPdf &pdf, RooAbsData &data, std::
 
 } // namespace
 
-namespace RooFit {
-namespace FitHelpers {
+namespace RooFit::FitHelpers {
 
 void defineMinimizationOptions(RooCmdConfig &pc)
 {
@@ -445,11 +444,11 @@ void defineMinimizationOptions(RooCmdConfig &pc)
    pc.defineInt("doSumW2", "SumW2Error", 0, minimizerDefaults.doSumW2);
    pc.defineInt("doAsymptoticError", "AsymptoticError", 0, minimizerDefaults.doAsymptotic);
    pc.defineInt("maxCalls", "MaxCalls", 0, minimizerDefaults.maxCalls);
-   pc.defineInt("doOffset", "OffsetLikelihood", 0, 0);
-   pc.defineInt("parallelize", "Parallelize", 0, 0); // Three parallelize arguments
-   pc.defineInt("enableParallelGradient", "ParallelGradientOptions", 0, 0);
-   pc.defineInt("enableParallelDescent", "ParallelDescentOptions", 0, 0);
-   pc.defineInt("timingAnalysis", "TimingAnalysis", 0, 0);
+   pc.defineInt("doOffset", "OffsetLikelihood", 0, minimizerDefaults.doOffset);
+   pc.defineInt("parallelize", "Parallelize", 0, minimizerDefaults.parallelize); // Three parallelize arguments
+   pc.defineInt("enableParallelGradient", "ParallelGradientOptions", 0, minimizerDefaults.enableParallelGradient);
+   pc.defineInt("enableParallelDescent", "ParallelDescentOptions", 0, minimizerDefaults.enableParallelDescent);
+   pc.defineInt("timingAnalysis", "TimingAnalysis", 0, minimizerDefaults.timingAnalysis);
    pc.defineString("mintype", "Minimizer", 0, minimizerDefaults.minType.c_str());
    pc.defineString("minalg", "Minimizer", 1, minimizerDefaults.minAlg.c_str());
    pc.defineSet("minosSet", "Minos", 0, minimizerDefaults.minosSet);
@@ -1115,7 +1114,6 @@ std::unique_ptr<RooFitResult> fitTo(RooAbsReal &real, RooAbsData &data, const Ro
    return RooFit::FitHelpers::minimize(real, *nll, data, pc);
 }
 
-} // namespace FitHelpers
-} // namespace RooFit
+} // namespace RooFit::FitHelpers
 
 /// \endcond