Text/plain form payloads have entries separated by a \r\n newline, but the HTML specification (https://html.spec.whatwg.org/#plain-text-form-data) requires there to be a final \r\n newline, which WebKit skips. Tests: https://wpt.fyi/results/html/semantics/forms/form-submission-0/text-plain.window.html?label=pr_head&max-count=1&pr=26740 (ignore the "formdata event" tests, since those are meant to test entries added to the form entry list through the formdata event, which WebKit doesn't yet implement)
<rdar://problem/73475295>
Created attachment 444180 [details] Patch
Created attachment 444207 [details] Patch
Created attachment 444292 [details] Patch
Committed r286221 (244602@main): <https://commits.webkit.org/244602@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 444292 [details].