[Core-AAM] Update searchbox mapping for ATK/AT-SPI2 to match IA2

[spectranaut]

Closes w3c/core-aam#241

Test, Documentation and Implementation tracking

Once this PR has been reviewed and has consensus from the working group, tests should be written and issues should be opened on browsers. Add N/A and check when not applicable.

• "author MUST" tests: n/a
• "user agent MUST" tests: [Core-AAM] Add test for update searchbox mapping for ATK/AT-SPI2 web-platform-tests/wpt#49551
• Browser implementations (link to issue or commit):
  • WebKit: n/a
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1932843
  • Blink: https://issues.chromium.org/u/3/issues/380295077
• Does this need AT implementations? no
• Related APG Issue/PR: n/a
• MDN Issue/PR: n/a

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