Since the current computation of what is a new line or not is wrong in some cases for Short living branches and Pull Requests, we need to update the way we compute it by passing an optional flag isNew in the response of the WS api/sources/lines.
On the UI side, if the flag does exists we use it to display the line correctly, otherwise we fallback to the old computation method based on the leak period and scm dates.
In api/sources/lines, an extra flag will be added for every line to indicate whether that line is new.
The definition of "new" depends on the context. For P/Rs and SLB, it's new compared to the target branch. For long lived branches it's new in the leak period.