Greptile P1: sedScriptParts stopped at -- and discarded the remaining
operands, so 'sed -- <script>' skipped script collection entirely. GNU sed
4.9 (verified): with no -e/--expression anywhere, the first operand after --
is the script and an s///e in it still executes.
The operands after -- are now collected as positionals, so the existing
first-positional-becomes-script rule applies. Operands after the script stay
file names (data). 2 regression tests pin both sides. Suite: 812/812.