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

web/components/action-buttons/ActionButtonMenu/ActionButtonMenu.module.scss

@@ -7,7 +7,6 @@
   display: flex;
   align-items: center;
   height: 100%;
-  padding-bottom: 16px; // to match antd nav margin-bottom
 
   button {
     height: 100%;