Decouple aliases from pass names

[rachitnigam]

We should decouple the alias mechanism from pass names. An alias should also configure compiler options like the sharing thresholds. This will let us define things like “-opt-size” which configures the pass pipeline to reduce the resource usage as aggressively as possible.

This will require some redesign of the pass manager but that is long overdue anyways with other UX issues.

[sampsyo]

Sounds wise!