Define pprinter for a new-assem:ssemble

Describe the feature

Add a pprinter for the new-assem:assemble function.

Is there a prototype?

No.

Describe the feature in more detail

As shown in !202 (comment 14117), the pprinter for assemble has the body indented quite a bit. I think it should not indent the body so much. The body should only be indented by 2 spaces. Maybe the function name (xoroshiro-update) could be indented by 4 spaces, but 2 spaces would be ok too.

Indenting the function name by 4 then makes the printed output like how multiple-value-bind is printed. That might be good enough.