cmd/compile: generic type alias useable without instantiation

[griesemer]

Compiling this program (with GOEXPERIMENT=aliastypeparams)

package p

type A[P any] func()
type B[P any] = func()
type C[P any] = B[P]

var _ = A(nil) // ERROR "cannot use generic type A without instantiation"
var _ = B(nil)
var _ = C(nil)

reports only one error (for A). There should be an error for each of A, B, and C.

[griesemer]

Related to #67547.
cc: @findleyr

[gopherbot]

Change https://go.dev/cl/588855 mentions this issue: go/types, types2: report error when using uninstantiated signature alias