Support isProperty query in DataMirror. (backport #3783) (#3790)

* Support isProperty query in DataMirror. (#3783)

This adds an API to DataMirror to query if a Data is a Property.

(cherry picked from commit 3b27dcdb

)

# Conflicts:
#	src/test/scala/chiselTests/reflect/DataMirrorSpec.scala

* Fix backport merge conflict.

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Co-authored-by: Mike Urbach <mike.urbach@sifive.com>