Track summary allow for true "update" clarify a bit the different purpose of methods

This comes after !36404 (merged) and !36509 (merged) It adress my main comment on the later

In practice separate filling of a TrackSummary from creating it. The create summary does the same thing but creates and fills. So there is also an update that can fill existing , without cloning.

This gives us kind of 3 families of methods

1. Method taking a non const track and update the track with a new summary (can use the old as starting point), not the summary. The main one is computeAndReplaceTrackSummary and the other is updateTrack. These since the previous MR can start from an existing Summary. But will not just return it. They will still clone/allocated a new one. But can add information. This is kind of the importand bit of !36509 (merged) so left it as is.

2. A method that actually updates the tracksummary. Does not clone and update the track, but updates the summary in place if there. This is the new ```updateTrackSummary`` And this is the thing I kind of prefer to have for the GSF ( also mentioning @amorley).

3. Methods taking const track arg, and returning owning pointer.These can never modify the input. They act as the "create part" of family 1 , i.e will call create.

Also mentioning @sroe

Not real change expected RunTier0Tests.log