implement packed struct equality

[Rexicon226]

closes #21678

[andrewrk]

Nice!

[rohlem]

I don't see an explicit mention (nor test) of this, but IMO a == b should still be a compile error if @TypeOf(a) != @TypeOf(b).
I assume the unchanged parts of the code already provide this behavior?

[Rexicon226]

I don't see an explicit mention (nor test) of this, but IMO a == b should still be a compile error if @TypeOf(a) != @TypeOf(b). I assume the unchanged parts of the code already provide this behavior?

It's a compile error because comparisons are peer resolves, and two different packed structs types cannot coerce into each other.

[Rexicon226]

@andrewrk will you write the release notes or should I?