Better error messages for unserializable annotations (bp #1885) (#1886)

* Better error messages for unserializable annotations (#1885)

(cherry picked from commit 47c81ee3

)

# Conflicts:
#	src/main/scala/firrtl/annotations/AnnotationUtils.scala
#	src/test/scala/firrtlTests/annotationTests/JsonProtocolSpec.scala

* Fix conflicts

Co-authored-by: Jack Koenig <koenig@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>