Fix mixed -E and -e emission (bp #1512) (#1518)

* Add test of mixing -e with -E in FirrtlMainSpec

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
(cherry picked from commit ffee96ba

)

* Check EmitAnnotation class before emitting

Fixes a bug where an Emitter was only checking for the presence of an
EmitCircuitAnnotation or EmitAllModulesAnnotation to control its
emission flavor (one-file-per-module or one-file). This changes the
check to ensure that the class of emitter matches that of the
annotation. This allows for correct behavior when mixing different
emitters, e.g., -E high -e middle.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
(cherry picked from commit a49a2f5e

)

# Conflicts:
#	src/main/scala/firrtl/Emitter.scala

* Fix backport failure

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
Co-authored-by: Edward Wang <edward.c.wang@compdigitec.com>