[dev.typeparams] cmd/compile: make HasShape() more efficient by implementing with a type flag

Implement HasShape() similar to how HasTParam() is implemented.

Fixes #47456

Change-Id: Icbd538574237faad2c4cd8c8e187725a1df47637
Reviewed-on: https://go-review.googlesource.com/c/go/+/339029


Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>