[ATSPI] Modal element containing only StaticText is ignored

https://bugs.webkit.org/show_bug.cgi?id=246329

Reviewed by Carlos Garcia Campos.

A modal element will not be set as the current modal when it has no
accessible content. But when using AT-SPI, an object with
AccessibilityRole::StaticText is ignored, since we expect its parent
to implement org.a11y.atspi.Text interface itself.

Fixes `accessibility/custom-elements/modal.html` time out.

* Source/WebCore/accessibility/AXObjectCache.cpp:
(WebCore::AXObjectCache::modalElementHasAccessibleContent):

Canonical link: https://commits.webkit.org/257235@main

Source/WebCore/accessibility/AXObjectCache.cpp

@@ -300,6 +300,14 @@ bool AXObjectCache::modalElementHasAccessibleContent(Element& element)
             if (auto* axObject = getOrCreate(node)) {
                 if (!axObject->computeAccessibilityIsIgnored())
                     return true;
+
+#if USE(ATSPI)
+                // When using ATSPI, an accessibility object with 'StaticText' role is ignored.
+                // Its content is exposed by its parent.
+                // Treat such elements as having accessible content.
+                if (axObject->roleValue() == AccessibilityRole::StaticText)
+                    return true;
+#endif
             }
 
             // Don't descend into subtrees for non-visible nodes.