cmd/compile: prevent typecheck importer reading type parameter twice

This is a port of CL 349009 to typecheck importer.

Fixes #48306

Change-Id: Iec3f078089346bd85f0ab739896e079940325011
Reviewed-on: https://go-review.googlesource.com/c/go/+/349011


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>