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/modals/ChatModal/ChatModal.module.scss

@@ -0,0 +1,12 @@
+.modalWrapper {
+  // This is so modals and popovers spawned from this modal will
+  // be on top of it. Modals usually have a z-index of 1000 and popovers 800.
+  // We're getting into really hacky territory here. Don't judge, there
+  // is history behind this. Ask an elder to tell you tales.
+  z-index: 799;
+  top: unset;
+}
+
+.root {
+  // margin-top: 18vh;
+}