[WebGPU] std::optional<To> convertFloat(From value) does not work for negative values
<rdar://problem/117553304>
Pull request: https://github.com/WebKit/WebKit/pull/19609
Committed 269835@main (5d2b2aa7ae7a): <https://commits.webkit.org/269835@main> Reviewed commits have been landed. Closing PR #19609 and removing active labels.