Move thin scrollbars to show only after scrolling has started and not on touchstart.

[skrustev]

In the new iOS 13 when clicking some element inside igScroll's content it cancels transitions too fast for the scrollbar animations and causes native events instability.

Closes issue with ID 267598

Additional information (check all that apply):

• [x] Bug fix
• [ ] New functionality
• [ ] Documentation
• [ ] Demos
• [ ] CI/CD

Checklist:

• [x] All relevant tags have been applied to this PR
• [ ] This PR includes unit tests covering all the new code
• [ ] This PR includes API docs for newly added methods/properties
• [ ] This PR includes general feature table updates in the root README.MD
• [ ] This PR contains breaking changes
• [ ] This PR includes behavioral changes and the feature specification has been updated with them

[coveralls]

Coverage decreased (-0.007%) to 84.02% when pulling f98107b6276b555105da8fc68f8db697054f697a on skrastev/fix-267598-19.2 into ba2a81cf390c102943c347d7a6a1dc15c2c4dd18 on 19.2.