Cut line in edit

[steff-o]

Is your feature request related to a problem? Please describe.
When a line is too long, the only way of shorten it is to delete each vertex from the end. Also, if a line feature needs to be split in two, the only solution is to draw a new line for one of the parts and trim vertices from the other or draw two new lines.

Describe the solution you'd like
A cut line tool. When active, clicking on a line will split the line in two which will result in two features, one with the first part of the line and the other with the last part and both will have the same attributes.

Not sure how to activate it though. The obvious solution would be to use a modifier key (shift, ctrl, alt or whatever combination isn't already used) when clicking a line that is selected for modification, but that would not work well on mobile devices. Maybe not a problem as not many will do serious precision editing on a touch screen. Alternatively a new tool would be added to the edit menu when a feature is selected for modification.

Describe alternatives you've considered
Let the end users suffer.

Additional context
The same could be applied to the draw tools, but has not been requested by the users, so it's beyond the scope of this issue.

The approach on how to activate this functionality would probably be similar to that of #2072