go/types, types2: qualify named types in error messages with type kind

go/types, types2: qualify named types in error messages with type kind

Change the description of an operand x that has a named type of sorts
by providing a description of the type structure (array, struct, slice,
pointer, etc).

For instance, given a (variable) operand x of a struct type T, the
operand is mentioned as (new):

        x (variable of struct type T)

instead of (old):

        x (variable of type T)

This approach is also used when a basic type is renamed, for instance
as in:

        x (value of uint type big.Word)

which makes it clear that big.Word is a uint.

This change is expected to produce more informative error messages.

Fixes #69955.

Change-Id: I544b0698f753a522c3b6e1800a492a94974fbab7
Reviewed-on: https://go-review.googlesource.com/c/go/+/621458
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>