Function prepareExpandedExpression

CvPlot/ext/catch2/inc/catch.hpp:15433–15435

namespace Catch {
    void prepareExpandedExpression(AssertionResult& result) {
        result.getExpandedExpression();
    }

    // Because formatting using c++ streams is stateful, drop down to C is required
    // Alternatively we could use stringstream, but its performance is... not good.