cmd/dist: add tests using the typeparams build tag

Now that go/ast changes have been guarded behind the typeparams build
tag, we no longer have coverage for tests involving generic code.

Add a new testing step to cmd/dist to run go/... and cmd/gofmt tests
using -tags=typeparams.

Comment out parser object resolution assertions that currently fail, and
which will be fixed by CL 304456.

Fixes #44933

Change-Id: I481dd4246a016f410307865b6c6c2bb3c8e6e3bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/310071


Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>