Fix silent module load failure in Chrome 86-93 due to missing VideoDecoder.isConfigSupported

[YoongiKim]

Summary

Fixes #2060

Chrome 86–93 shipped VideoDecoder as part of an origin trial but did not include VideoDecoder.isConfigSupported — that method was only added in Chrome 94. The existing guard in _checkWebCodecsH264DecodeSupport() checked for VideoDecoder in window but not for isConfigSupported on the constructor, causing a "is not a function" error at the top-level await call site. Because this happens during ES module evaluation, the entire module silently fails to load with no console error — just a blank page.

Change

// Before
if (!('VideoDecoder' in window)) {
    return false;
}

// After
if (!('VideoDecoder' in window) ||
    !('isConfigSupported' in VideoDecoder)) {
    return false;
}

This makes the function gracefully return false on browsers that have VideoDecoder but lack isConfigSupported, instead of throwing.

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