Proposal: allow `erased` to be used in place of a definition

[japgolly]

Instead of:

erased given CanThrow[Ex1] = ???

which is confusing to newbies and requires even experienced users to take a deep breath, what do you think about allowing the erased keyword itself to stand in as a fake definition? It would look like this:

erased given CanThrow[Ex1] = erased

[japgolly]

If the above is acceptable, then a potential next step could be to have to compiler apply the erased flag to any definition with erased as the body,

given CanThrow[Ex1] = erased

[nicolasstucki]

We already have this feature.

It is exposed as the method scala.compiletime.erasedValue.

erased given CanThrow[Ex1] = erasedValue

[abgruszecki]

@nicolasstucki I guess this issue can be closed then, no?

[japgolly]

Linking to #11739