Avoid the common qMin/qMax errors when having qreal as floats

When building qt applications with qreal being floats you almost always run into compiler errors with qMax/qMin being called with double/float or v.s. This is also the case for the Qt code base itself ( see QTBUG-69573 ).

This type of problem could be avoided in general by introducing special versions of qMin/qMax - something like this:

inline qreal qMin( float v1, double v2 )  {  return qMin( double( v1 ), v2 ); }

inline qreal qMin( double v1, float v2 ) { return qMin( v1, double( v2 ) ); }

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