Add --dump-fir option to ChiselStage (backport #3453) (#3456)

* Add --dump-fir option to ChiselStage (#3453)

This option will dump the .fir before invoking firtool.

Additional changes:
* Use os.lib for invoking firtool
* Use lazy serialization to avoid holding the entire FIRRTL in
  memory.
* Mix NoStackTrace into FirtoolNotFound
* Fix detection of no firtool

(cherry picked from commit 4db86b2f

)

# Conflicts:
#	src/main/scala/circt/stage/CIRCTOptions.scala
#	src/main/scala/circt/stage/ChiselStage.scala
#	src/main/scala/circt/stage/phases/CIRCT.scala

* Resolve backport conflicts

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Co-authored-by: Jack Koenig <koenig@sifive.com>