go/parser: move type params in scope for the function signature

Type parameter resolution is a bit tricky: type parameters are in the
function scope, but unlike ordinary parameters may reference eachother.
When resolving the function scope, we must be careful about the order in
which objects are resolved and declared.

Using ordering allows us to avoid passing around temporary scopes for
field declarations.

Add a bunch of tests for this behavior, and skip "_" in resolution tests
as it just adds noise.

For #45221

Change-Id: Id080cddce3fd76396bf86ba5aba856aedf64a458
Reviewed-on: https://go-review.googlesource.com/c/go/+/304456


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