`FocusManager` can get out of sync with the DOM with Firefox and Safari

[BenHenning]

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Description

RaspberryPiFoundation/blockly-keyboard-experimentation#87 has much more context, but essentially it's possible for FocusManager to desync with the DOM's focus specifically in Firefox and Safari in cases when a focused (possibly any) element is moved to a new location in the DOM. Chrome will fire a focus change event in these cases, but Firefox/Safari do not (or at least not in the same scenarios).

Reproduction steps

See RaspberryPiFoundation/blockly-keyboard-experimentation#87 for repro steps, though the fixed introduced in #9082 has to be temporarily removed in order to observe the problem.

Stack trace

None

Screenshots

No response

Browsers

Firefox desktop, Safari desktop