[FIREmitter] Export raw annotations as inline JSON

[dtzSiFive]

Consider adding support to exporter for printing out "rawAnnotations" as JSON array on circuit.

This would allow better round-tripping of designs containing annotations, and with firtool support to export before LowerAnnotations could move annotation files into the FIRRTL this way.

[seldridge]

See the example on #6628 for more information and an example of one annotation that would be relatively trivial to emit.