fix(Modal): exclude Poppers in aria-hidden change

Popper based components like Select or Dropdown get mounted to the DOM
on the same level as Modal. Modal then on update can set aria-hidden
label to true via function toggleSiblingsFromScreenReaders, which adds
the label to all the elements that are siblings of the Modal, including
these components.This causes the opened Popper based component to become
invisible for screen readers and/or Playwright.

Fix this by excluding all the Popper components from this function's
behaviour.

Author: tkoscieln

packages/react-core/src/components/Modal/Modal.tsx

@@ -111,7 +111,8 @@ class Modal extends Component<ModalProps, ModalState> {
     const target: HTMLElement = this.getElement(appendTo);
     const bodyChildren = target.children;
     for (const child of Array.from(bodyChildren)) {
-      if (child.id !== this.backdropId) {
+      const isPopperElement = child.hasAttribute('data-popper-placement');
+      if (child.id !== this.backdropId && !isPopperElement) {
         hide ? child.setAttribute('aria-hidden', '' + hide) : child.removeAttribute('aria-hidden');
       }
     }