x/exp/apidiff: support for go/types.Alias

[timothy-king]

golang.org/x/exp/apidiff should be updated to support go/types producing Alias nodes. This is required for these tools to type check input code containing type parameterized alias nodes (1.24).

Additionally golang.org/x/exp/cmd/{apidiff, gorelease} should have the gotypesalias=1 GODEBUG setting enabled by default when built with a toolchain >= 1.24. See https://go.dev/cl/627715 for an example of how to do this.

See #69772 for additional context.

[gabyhelp]

Related Issues

• go/types, x/tools: help tool authors support the new go/types.Alias node #67263
• x/tools/gopls: handle go1.22's go/types.Alias #64581 (closed)
• x/tools: get tests passing with GODEBUG=gotypesalias=1 #65294 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[adonovan]

@jba