Change closeTab icon from circled to squared

[cezaraugusto]

Auditors: @bsclifton

Fix #5431

• 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).

Last attempt to fix this had a report by @luixxiul and @srirambv that close icon had a clickable area outside icon itself (which were circled). I did a local fix which included replacing <span> with <map> + <area> (so the linkable area could be rounded as well), but needed an image instead of a fontAwesome icon. While asking for a new one @bradleyrichter suggested a new icon, which solved issue anyway:

Test Plan:

• Automated tests must still pass:

npm run test -- --grep="tabContent components"

QA Steps:

• You should only close a tab if you intentionally hit the close button.

[bsclifton]

Really close (and wow- this looks good!)

Here's a breakpoint I found where the tab's close button became very skinny and almost unclickable:

[cezaraugusto]

thanks, fixed

[bsclifton]

Changes look great! 😄 Nice work