[Win] Use Win32Handle for m_fileMapping of WTF::FileSystem::MappedFileData
Pull request: https://github.com/WebKit/WebKit/pull/14320
Committed 264502@main (f0c80d6f8576): <https://commits.webkit.org/264502@main> Reviewed commits have been landed. Closing PR #14320 and removing active labels.
<rdar://problem/109808514>