Investigate representation of source location of binary operations

In order to improve the accuracy of warnings for https://bugreports.qt.io/browse/QTBUG-124220, https://codereview.qt-project.org/c/qt/qtdeclarative/+/556186 stores the location of binary expressions for later use. The stored location is the combined location of the left operand, the operator, and the right operand, instead of just the operator. We should investigate which representation is best and whether the current on causes any issues.