[WebGPU] Use UnsignedWithZeroKeyHashTraits in m_cachedBindGroupLayouts instead of adding 1 to the key
<rdar://problem/109590315>
Pull request: https://github.com/WebKit/WebKit/pull/14126
Committed 264304@main (597aa395dcdc): <https://commits.webkit.org/264304@main> Reviewed commits have been landed. Closing PR #14126 and removing active labels.