Aggregate PriorityMux and Mux1H Seq size errors

[jackkoenig]

All I wanted to do was aggregate errors, but in for a penny, in for a pound.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• API Modification

Desired Merge Strategy

• Squash

Release Notes

• This requires adding source locators to PriorityMux and Mux1H which requires SourceInfoTransform macros in Scala 2 and thus splitting the Scala 2 / Scala 3 public interfaces.
• Because macro applications do not support named arguments in Scala 2, this is an API change.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[mikeurbach]

I'm a little out of the loops on the scala 2 vs. 3 splits, but this seems reasonable to me.