R1:df939f1337fd

Fix two issues with embedding other fields inside "Summary" or "Test Plan" in Differential with the web UI

Summary:
Ref T11114. Converting to EditEngine caused us to stop running this validation, since these fields no longer subclass this parent. Restore the validation.

Also, make sure we check the //first// line of the value, too. After the change to make "Tests: xyz" a valid title, you could write silly summaries / test plans and escape the check if the first line was bogus.

Test Plan: {F2493228}…