Golang cmd/compile, importers: implement support for Alias types nodes in export data format

This is a follow-up issue on #63223 to track the support for Alias types in importers. @mdempsky @findleyr

Comment From: griesemer

cc @mvdan

Comment From: gopherbot

This issue is currently labeled as early-in-cycle for Go 1.23. That time is now, so a friendly reminder to look at it again.

Comment From: mvdan

Just checking in - is this still planned for Go 1.23? Once it lands in master, I'm more than happy to give it a try :)

Comment From: griesemer

Yes. We're just super busy at the moment. Thanks.