This CL better abstracts away the parameter leak info that was
directly encoded into the uint16 value. Followup CL will rewrite the
implementation.

Passes toolstash-check.

Updates #33981.

Change-Id: I27f81d26f5dd2d85f5b0e5250ca529819a1f11c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/197679
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>