Treat ARIA treegrids as tables in browse mode (#11699)
* Chrome/Gecko: Render all content of ARIA treegrids in browse mode as a table.
* Gecko_ia2 bfubBackend: ensure that ARIA treegrids get a role of table as soon as possible, so that it presents exactly like a table in brwose mode and quick nav to the table also works.
* Fix linting issue
* speech.getControlFieldSpeech: treeview items which are not normally spoken at all, should at least have expanded / collapsed / level announced.
* Gecko vbufBackend: split fetching of IAccessible2 attributes into its own function.
* Gecko vbufBackend: clarify comment
* Gecko vbufBackend: split checking for xml roles into its own function.
* Gecko vbufBackend: populateMapWithIA2AttributesFromPacc is now createMapOfIA2AttributesFromPacc, and returns a map.
* Added system test for ARIA treegrid in browse mode.
* Fix linting issues
* system test for ARIA treegrid: use the actual html file from the w3c ARIA practices repository, rather than a local copy, as it is very likely we will want to use more of these test cases in future.
* System tests: fix get_speech_at_index_until_now so that each line (sequence) is stripped of whitespace at its beginning and end. Previously whitespace was only stripped from the ends of the entire multiline string.
* Fix linting issues
* ARIA treegrid system test: focus a link in the iframe before moving to the treegrid so as to not have to deal with a possible focus event on the iframe document when switching to focus mode in the treegrid later.
* system tests: _chrome.getSpeechAfterKey: wait for any new speech to finish after sending a key.
* Update what's new.
