move ir node defs into subpackage of ir

[patrick-schultz]

Change Description

Fixes #<issue_number> (delete if N/A)

Brief description and justification of what this PR is doing.

Security Assessment

Delete all except the correct answer:

• This change has a high security impact
  • Required: The impact has been assessed and approved by appsec
• This change has a medium security impact
• This change has a low security impact
• This change has no security impact

Impact Description

For none/low impact: a quick one/two sentence justification of the rating.

• Example: "Docs only", "Low-level refactoring of non-security code", etc.
  For medium/high impact: provide a description of the impact and the mitigations in place.
• Example: "New UI text field added in analogy to existing elements, with input strings escaped and validated against code injection"

(Reviewers: please confirm the security impact before approving)

[patrick-schultz]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [query] codegen all value ir node classes #14771
• move ir node defs into subpackage of ir #14783 👈 (View in Graphite)
• [query] move mill modules into subdirectory #14772 : 2 other dependent PRs (#14773 , #14796 )
• [query] remove *.out from .gitignore #14780
• [query] don't hardcode paths to test resources, cont'd #14779
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.