Refactor mobile chat into modal (#3038)

* feat(mobile): refactor mobile chat into modal

- Make page always scrollable
- Move mobile chat into a standalone modal

* fix(test): split out mobile browser test specs

* fix(mobile): force chat button to render on top of footer

* fix: some small updates from review

* fix: hide/show hide chat menu option based on width

* fix: chat button icon getting cut off

* chore(tests): add browser tests for mobile chat modal

* chore(tests): add story for ChatModal component

* fix(test): quiet shellcheck

* fix: remove unused import

* fix(tests): silence storybook linting warning

* fix(ui): reposition chat modal button icon with transform

test/automated/screenshots/run.sh

@@ -5,7 +5,9 @@ set -o errexit
 set -o pipefail
 
 finish() {
+	# shellcheck disable=SC2317
 	kill_with_kids "$BROWSERSTACK_PID"
+	# shellcheck disable=SC2317
 	kill_with_kids "$STREAM_PID"
 }