Move tabs toolbar mouseleave handler to parent element

[petemill]

… which does not use 'contents' value for display style property

Since a display: contents container will essentially be the width of its children, and the child was being removed on tab close, the width of the parent element was narrowing so that the mouse was no longer on top, but the mouseleave event did not fire. Moving this handler to a parent element fixes it. It encompasses the pinned tabs but this should not be an issue as the intention of the feature is to relate to the tabs bar as a whole.

Fix #14477

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).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed. (Ask a Brave employee to help if you cannot access this document.)

Test Plan:

On issue

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[bsclifton]

Works great! 😄 ++

[bsclifton]

master c4b18cd
0.24.x de04be9
0.23.x cc62793