Update min-threshold for closing a tab

[cezaraugusto]

• 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).

Resolves #8130

please don't squash, one commit is just for tests ✅

Test Plan:

1. Automated tests must pass for all tab content components:

# just to doublecheck -- not affected
npm run test -- --grep="Tabs content - AudioTabIcon"
npm run test -- --grep="Tabs content - Favicon"

# affected
npm run test -- --grep="Tabs content - PrivateIcon"
npm run test -- --grep="Tabs content - NewSessionIcon"
npm run test -- --grep="Tabs content - CloseTabIcon"
npm run test -- --grep="Tabs content - Title"

Manual Tests:

1. CloseTab icon must be visible for active tabs at 83px tab-size (largeMedium breakpoint)
2. CloseTab icon must not be visible (even on hover) for non-active tabs
3. Resizing a tab should be kept its content fluid without regressions nor bad UI

Test Plan:

1. Open tabs gradually
2. At some point, close tab icon should be fixed on active tab (83px tab-wide)
3. At that point, inactive tabs shouldn't have a close icon, unless you activate
4. Open some private/partitioned tab
5. Get around 30-40 tabs
6. Resize window
7. Tab content such as favicon, private/partitioned icons, and title should work as expected

[bradleyrichter]

Just tested and it's a great improvement. Approved my me...

[bsclifton]

++ killer job on the tests 😎 👍