Move all polls processing to events-sdk & prep for stable polls (#7517)

* Move all polls processing to events-sdk

This makes polls support the full range of extensible events (both parsing and generation).

* Appease the linter

* Fix & update tests

* Update events-sdk for polls bugfix

* Update events-sdk for typechecking

* Add missing type cast

* Update per review

package.json

@@ -89,7 +89,7 @@
     "lodash": "^4.17.20",
     "maplibre-gl": "^1.15.2",
     "matrix-analytics-events": "https://github.com/matrix-org/matrix-analytics-events.git#1eab4356548c97722a183912fda1ceabbe8cc7c1",
-    "matrix-events-sdk": "^0.0.1-beta.2",
+    "matrix-events-sdk": "^0.0.1-beta.6",
     "matrix-js-sdk": "github:matrix-org/matrix-js-sdk#develop",
     "matrix-widget-api": "^0.1.0-beta.18",
     "minimist": "^1.2.5",