Rename `valueOrThrow` and `valueOrNull`

  • Slice.valueOrNull is unnecessary because Either.orNull() already exists
  • Slice.valueOrThrow should be renamed Slice.orThrow() for cohesion with Either.orNull() and Either.orNone()
  • Introduce Slice?.orNull() and Slice?.orThrow()

After that, Ref.requestOrThrow and Ref.requestOrNull can be removed:

// before
val a = ref.requestOrThrow()
// after
val b = ref.request().orThrow()
Edited by Ivan “CLOVIS” Canet