getComputedStyle(element).textBoxEdge will return `leading leading`. However `leading leading` is an invalid value for `text-box-trim`. The `leading` value needs to be special cased so it only returns the value once.
<rdar://problem/117643064>
Pull request: https://github.com/WebKit/WebKit/pull/30171
Committed 280413@main (398e5e25e9f2): <https://commits.webkit.org/280413@main> Reviewed commits have been landed. Closing PR #30171 and removing active labels.