replacing points in a lineseries does not check if count changes

using the replace method to change the points of a lineseries, the count property of that series does not change, even though the number of points did change.

a possible solution is: connect the pointsReplaced signal to the handleCountChanged slot and check if the cound did change to emit the countChanged signal that updates the property in "src/chartsqml2/declarativelineseries.cpp".

the workaround is to clear the line series first, and then use append to add the points.