Add chisel3.stage.phases.Elaborate Phase

This adds an Elaborate Phase that expands ChiselGeneratorAnnotations
into ChiselCircuitAnnotations and deletes the original.

Co-Authored-By: Schuyler Eldridge <schuyler.eldridge@ibm.com>
Co-Authored-By: chick <chick@qrhino.com>
Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>