Add option to ignore undeserializable annotations (basically pass them through)

[jackkoenig]

Checklist

• Did you write out a description of the feature you want to see?
• Did you look around for any related features?
• Did you specify relevant external information?

Feature Description

Type of Feature

Related Features

External Information

[jackkoenig]

For implementing this, the basic problem is trying to deserialize a whole List[Annotation] at once:

firrtl/src/main/scala/firrtl/annotations/JsonProtocol.scala

Line 298 in ef1d27a

read[List[Annotation]](in)

To do this, we need to deserialize one-by-one.

This is basically the inverse of

firrtl/src/main/scala/firrtl/annotations/JsonProtocol.scala

Line 260 in ef1d27a

val safeAnnos = annos.map { anno =>

which is doing it for serialization (only used by logging).

[jackkoenig]

@davidbiancolin has noted that package-level allow and disallow lists may be useful here.