Prevent internal attributes from leaking

[Scott-Guest]

When we emit to KORE, user-defined groups [group(my-att)] end up being represented the same as [my-att]. Accordingly, we must report an error if a user-defined group conflicts with any built-in attribute. Unfortunately, this includes any undocumented internal-only attributes.

To address this, we can instead emit the user groups literally as \group{}("my-att"), but this will require updating any consumers downstream.

[Scott-Guest]

Blocked on #2625

If there is some built-in attribute my-att unintentionally missing from the whitelist, then this change will cause it to be emitted to KORE as \group{}("my-att"), breaking anything downstream depending on my-att.

To be safe then, we should wait until the whitelist is complete and the option to opt-out is removed before making this change.

[Scott-Guest]

Blocked until #3484 is merged

[Scott-Guest]

Closed by #3441