findbar clear button not working

[jkup]

• 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).

Fix #4965

Auditors @bbondy @bsclifton

Open the findbar, type some text and click the close button inside the input. The text should disappear.

Test Plan:

[bsclifton]

LGTM 😄 Holding off on merge since issue is marked as 0.12.7 (updating the PR to match)

[bbondy]

I'll take this in 0.12.6 thanks.