Qt WebEngine 5.15 is still vulnerable to CVE-2023-6345

This has been fixed in the 6.5 branch:

• https://codereview.qt-project.org/c/qt/qtwebengine/+/523361
• https://github.com/qt/qtwebengine-chromium/commit/a53b8f85debd5537b2775dd95dd2e41e30a9a66b

However, the vulnerability still exists in the 5.15 branch:

• https://github.com/qt/qtwebengine-chromium/blob/ce00f9b5aa761866b24d6460e10aacb671c92cf0/chromium/third_party/skia/src/gpu/ops/GrDrawVerticesOp.cpp#L760

(The code has moved around a bit between Chromium 87 and Chromium 108)