x/pkgsite: allow short one line "code" blocks / declaration to line wrap

[thomasf]

godoc.org does it

pkg.go.dev does not:

I don't know what metric or categories should be used to decide when to allow line wrapping because for multi line code blocks i would probably not th but I think it needs to be addressed.

[gopherbot]

Change https://golang.org/cl/279726 mentions this issue: content: wrap functions and methods