1. Make ia2AccessibleText::UpdateTextChangeData (and sLastTextChangeAcc) use HyperTextAccessibleBase instead of HyperTextAccessibleWrap.
2. Make ProxyTextChangeEvent call UpdateTextChangeData when the cache is enabled.
3. Don't send sync text change events when the cache is enabled. They don't need to be sync because clients query the cache, not the content process a11y tree. Even if the content process a11y tree mutates, the cache can't update until in-process clients have synchronously handled the event.
Differential Revision: https://phabricator.services.mozilla.com/D139677
d2d7992aaf