[Glitch] Fix page incorrectly scrolling when bringing up dropdown menus

Port e88a05f707 to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/components/dropdown_menu.js

@@ -46,7 +46,7 @@ class DropdownMenu extends React.PureComponent {
     document.addEventListener('keydown', this.handleKeyDown, false);
     document.addEventListener('touchend', this.handleDocumentClick, listenerOptions);
     if (this.focusedItem && this.props.openedViaKeyboard) {
-      this.focusedItem.focus();
+      this.focusedItem.focus({ preventScroll: true });
     }
     this.setState({ mounted: true });
   }

app/javascript/flavours/glitch/features/compose/components/dropdown_menu.js

@@ -64,9 +64,9 @@ export default class ComposerOptionsDropdownContent extends React.PureComponent
     document.addEventListener('click', this.handleDocumentClick, false);
     document.addEventListener('touchend', this.handleDocumentClick, withPassive);
     if (this.focusedItem) {
-      this.focusedItem.focus();
+      this.focusedItem.focus({ preventScroll: true });
     } else {
-      this.node.firstChild.focus();
+      this.node.firstChild.focus({ preventScroll: true });
     }
     this.setState({ mounted: true });
   }