internal/apidiff: support materialized aliases

(The previous CL 559935 was insufficient.)

Also, improve test output.

Updates golang/go#65294

Change-Id: I05cafadce0dd6f18ff66d2ca462a3eb546c4ca81
Reviewed-on: https://go-review.googlesource.com/c/tools/+/577576
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: adonovan

go.mod

@@ -10,6 +10,8 @@ require (
 
 require golang.org/x/sync v0.7.0
 
+require github.com/google/go-cmp v0.6.0 // indirect
+
 require (
 	golang.org/x/sys v0.19.0 // indirect
 	golang.org/x/telemetry v0.0.0-20240228155512-f48c80bd79b2

go.sum

@@ -1,3 +1,5 @@
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/yuin/goldmark v1.4.13 h1:fVcFKWvrslecOb/tg+Cc05dkeYx540o0FuFt3nUVDoE=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/mod v0.17.0 h1:zY54UmvipHiNd+pm+m0x9KhZ9hl1/7QNMyxXbc6ICqA=