Fix CurveEdit not notifying about all changes

[passivestar]

Closes #103831

Unlike Curve::set_point_value(), Curve::set_point_offset() doesn't mark curve as dirty which causes problems with CurveEdit::set_point_position() that calls them out of order and causes CurveTexture resource to not use the latest data of its Curve

This could be solved by adding mark_dirty() to Curve::set_point_offset but that would double the amount of calls to heavy CurveTexture::_update. So instead we're reversing the order of calls in CurveEdit::set_point_position. I made sure set_point_value is using the correct index (it's known in advance because drag has already happened)

[aryan-11825114]

I also opened a P.R. to close this issue, see #96296.
Also closes #95752.