Feature proposal: Selector language

[johanste]

We have quite a few use cases where there is a need to select a set of types based on some criteria. A simple example of this is the @@ augment syntax in #218 (which in the current proposal only supports selecting by identity). Other examples include type constraints, emitters and validators.

There may be benefit of providing a common way to express such selectors. I believe @bterlson may have additional use cases up his sleeve.

[markcowl]

pri: 1

[johanste]

This also came up in the context of being able to mark everything in a namespace as @removed (for massively breaking changes/redefinition of a service)