Rename "Passive" to "Simplex" [RFC]

[mwachs5]

The FIRRTL spec names types that all have the same direction with no flipped-ness as "passive" (https://github.com/chipsalliance/firrtl-spec/blob/e7199fcc219bbc6e8bf9f380dc15dcdac20961c2/spec.md#passive-types). In other words this is the opposite of "Duplex". In english "Passive" and "Duplex" do not seem like intuitive opposites. Would "Simplex" Be a better term? Or is there some implied meaning of "Active vs Passive", but "Active" does not appear in the spec except in the context of read/write ports which seems like a very different concern,

Duplex is currently defined in contrast with "sink" and "source" for Flows, so not sure if this is an appropriate substitution of saying "anything not sipmlex is duplex" since passive is talking about the type not the particular hardware (Node, reg, port, etc).