Add Bundle.Init (analogous to VecInit / Bundle.Lit)

I sketched out a version of this here: https://scastie.scala-lang.org/D0948BD1SgeZEqLGkVBoJg

Ideally this (and VecInit for that matter) would:

1. compose
2. utilize DataView -- (we probably cannot change VecInit but views here so that you can connect to the underlying fields would be nice)

Regardless, this sketch is useful on its own even without the more robust solution

Type of issue: bug report | feature request | documentation | other enhancement

Impact: API addition (no impact on existing code)

Development Phase: proposal

What is the use case for changing the behavior?

Useful API for users