Fix dropdown menu positions when scrolling (#22916)

* Update react-overlays to latest version

* Fix breaking changes in dropdown menus

* Use react-overlays built-in arrow positioning feature
* Re-implemented `.dropdown-menu__arrow` to have a defined width and height to improve positioning
* Moved wrapping div (`.dropdown-menu` from `DropdownMenu` to `Dropdown`)
* Wrap button in a span to solve issue with ref
* Temporarily remove animations

* Fix breaking changes in emoji picker

* Wrap EmojiPickerMenu in a div where react-overlays’ ref is added

* Fix breaking changes in language dropdown

* Fix breaking changes in privacy dropdown

* Fix breaking changes in search form

* Add animations back using `@keyframes`

* Fix arrow color in light theme

* Fix linting issue

* Remove unused `mounted` state

* Remove `placement` state from components and redux

And remove the placement state from props of the menu components.

* Remove abolution position to fix flip issue

* Remove z-index to fix modals and overlay positions

* Fix lint issues

* Set placement in privacy and language components

Copy the placement state into the `PrivacyDropdown` and `LanguageDropdown` components, to apply correct styling to the buttons depending on which placement the Overlay has.

* Move `placement` state to correct component

package.json

@@ -98,7 +98,7 @@
     "react-intl": "^2.9.0",
     "react-motion": "^0.5.2",
     "react-notification": "^6.8.5",
-    "react-overlays": "^0.9.3",
+    "react-overlays": "^5.2.1",
     "react-redux": "^7.2.9",
     "react-redux-loading-bar": "^5.0.4",
     "react-router-dom": "^4.1.1",