Additional debouncer fixes

[kevinpschaaf]

Additional updates to #5499 and #5508 based on internal testing:

• Don't clear set at the end for flushDebouncers reentrancy robustness (they will be deleted from queue when they run, so queue should always be empty when forEach returns.
• Remove debouncer from queue before running debouncer callback, to protect against callback calling flush()

Reference Issue

Fixes #5250