We have several checked type assertions to *types.Named in both cmd/cloner and cmd/viewer.
As Go 1.23 updates the go/types package to produce Alias type nodes for type aliases,
these type assertions no longer work as expected unless the new behavior is disabled
with gotypesalias=0.
In this PR, we add codegen.NamedTypeOf(t types.Type), which functions like t.(*types.Named)
but also unrolls type aliases. We then use it in place of type assertions in the cmd/cloner and
cmd/viewer packages where appropriate.
We also update type switches to include *types.Alias alongside *types.Named in relevant cases,
remove *types.Struct cases when switching on types.Type.Underlying and update the tests
with more cases where type aliases can be used.
Updates #13224
Updates #12912
Signed-off-by: Nick Khyl <nickk@tailscale.com>
03acab2639