[5.x] Matrix field conditional display for entry types

[turnstylerj]

One of the features I'm missing from Neo with the new Matrix is the ability to conditionally display Entry Types. It's common to have a handful of "core" Entry Types and a few that are only used on one or two entries; we typically give the author a default set of Entry Types for simplicity on day-to-day entry creation, then an advanced option that enables the one-off/all Entry Types.