Fix search icon overlapping custom search engine icon

[bsclifton]

• 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 search icon overlapping custom search engine icon

• Fixes Search icons overlapping with urlbar find icon #5477
• Accidental regression caused by Updating icons in URL bar #5449
• Includes webdriver test to enforce the expected behavior

Auditors: @bbondy

Test Plan:

1. Launch Brave and open a new tab
2. Confirm that magnifying glass shows
3. Type into URL bar, confirm it stays as magnifying glass
4. Use a search shortcut, like :m, and type this into the URL bar. For example :m date
5. magnifying glass should disappear and it should show the MDN icon

[bbondy]

++ thanks, and thanks for the extra test too.