Reintroduce #19714: 'Send a SSS response immediately if the config has changed and there are new results to sync'

[reivilibre]

#19714 had to be reverted because it aggravated #18880, causing performance problems.

Removing device_one_time_keys_count and device_unused_fallback_key_types from the __bool__ check on E2eeExtension appeared to resolve the problem, but needs proper consideration and review.