visionOS: Make sure the multiview caps is enabled

The caps for visionOS are the same as for macOS, so just set the
same for both, including support for multiview.

Task-number: QTBUG-126294
Change-Id: Ie3a551f134d8a8a39d63801bc7fd8dcca1e715c9
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit 2c2d36f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/rhi/qrhimetal.mm

@@ -600,7 +600,7 @@ inline Int aligned(Int v, Int byteAlign)
     const QString label = QString::asprintf("Qt capture scope for QRhi %p", this);
     d->captureScope.label = label.toNSString();
 
-#if defined(Q_OS_MACOS)
+#if defined(Q_OS_MACOS) || defined(Q_OS_VISIONOS)
     caps.maxTextureSize = 16384;
     caps.baseVertexAndInstance = true;
     caps.isAppleGPU = [d->dev supportsFamily:MTLGPUFamilyApple7];