[WIP] make use of mouse velocity for vertical tab preview

[cezaraugusto]

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run indivually or as a suite ref

This is a work in progress. However, look-and-feel is already testable if you wish.

Auditors: @bradleyrichter

[bradleyrichter]

I found a few bugs to look at:

1. It seems easy to get it into a state where the tab is selected by hover and not mouse click.

2. Possibly related to Basic tab structure #1, but the tab can enter a state where the tab text and title bar are correct but the DOM content are from a different tab

example:

3. My first tab would not show a preview for a while

4. leaving focus and returning caused tabs to be preview-able but not clickable.

[cezaraugusto]

yes as we talked I think this is a different issue and more related to #8842.

[cezaraugusto]

after taking this step for ~2 weeks I don't think this will ever work as-is so I'll close. I have a better solution.