Indicate more obviously that a matrix has more columns than it currently displays

[RomanTsukanov]

When all matrix columns do not fit into the container, a horizontal scrollbar appears. However, it is almost unnoticeable (look at the picture below). Maybe we could come up with a way to indicate that there are hidden columns more obviously.

[JaneSjs]

This task is related to the following issue: https://github.com/surveyjs/survey-library/issues/6468.