Skip the Shift+Tab panel click test in macOS WebKit (#15232)

The test holds Shift+Tab, plus Option in WebKit so that Tab reaches
links, then clicks a textarea in a tabset panel. On macOS, WebKit does
not focus a control clicked while Option is held: a probe run showed
pointerdown, mousedown and click reaching the textarea, none of them
cancelled, with no focus change and the panel left selected. With
Option released, the same click focuses the textarea. The tabset code
does not take part, so the nightly macOS failure is a WebKit platform
behavior, not a regression.

Releasing Option before the click would make the test pass but empty
it: the tabset script ends its Shift+Tab state on any keyup, so the
click would no longer check that pointerdown ends it. The test is
skipped for WebKit on macOS only; Linux WebKit, Chromium and Firefox
keep the check.

Author: cderv

tests/integration/playwright/tests/revealjs.spec.ts

@@ -472,6 +472,11 @@ test.describe('tabset keyboard focus order', () => {
   });
 
   test('clicking a panel control while Shift+Tab is held keeps that panel', async ({ page, browserName }) => {
+    // On macOS, WebKit does not focus a control clicked while Option is held,
+    // and WebKit needs Option to Tab to links. Releasing Option first would not
+    // help: any keyup ends the Shift+Tab state this test is about.
+    test.skip(browserName === 'webkit' && process.platform === 'darwin',
+      'macOS WebKit does not focus an Option-click');
     await gotoSlide(page, '#/control-handling-tab-in-a-tabset');
     await link(page, 'a second link').focus();
     await page.keyboard.down('Shift');