Add Offset for TouchLineBarSpot in touchCallback response

**Is your feature request related to a problem? Please describe.**
Currenly I can show custom tooltip for needed spot. However, I only have access to offset of event coming from touchCallback. Which creates an issue of showing tooltip exactly on the spot offset.
I tried to redefine distanceCalculator, but it didn't help.

**Describe the solution you'd like**
Would be nice to get the spot Offset from touchCallback response [TouchLineBarSpot].

Start by tracing the TouchLineBarSpot type and the touchCallback response described in the issue. Determine where the spot's offset should be exposed, then verify that a custom tooltip can use it and that existing chart behavior remains intact.

Written by the indexing model from the issue text.