Allow passing the inline jq script before --

jq previously only allowed passing the inline script before -- (as if
they were options) even though one would expect the inline script to be
a positional argument.

Since jq previously also refused to run with a usage error if the script
was passed after -- (It was not assuming  .  as script as it does when
no arguments are passed), and positional arguments are allowed before --
and even before other options, it should not be a breaking change to
change that weird behaviour, and allow the script to appear after --.

It also simplifies the option parsing code a bunch.

Fixes #2918

jq.1.prebuilt

@@ -250,7 +250,7 @@ Output the jq help and exit with zero\.
 \fB\-\-\fR:
 .
 .IP
-Terminates argument processing\. Remaining arguments are positional, either strings, JSON texts, or input filenames, according to whether \fB\-\-args\fR or \fB\-\-jsonargs\fR were given\.
+Terminates argument processing\. Remaining arguments are not interpreted as options\.
 .
 .TP
 \fB\-\-run\-tests [filename]\fR: