Add opt-in AutoCloneType for Records (backport #2781) (#2785)

* Add opt-in AutoCloneType for Records (#2781)

There is a new trait, chisel3.experimental.AutoCloneType that is mixed
in to Bundle and can optionally be mixed in to user-defined Records. The
compiler plugin prints a deprecation warning on any user-defined
implementation of cloneType, telling the user to mix in AutoCloneType
before upgrading to 3.6.

(cherry picked from commit a234fd48

)

# Conflicts:
#	core/src/main/scala/chisel3/Aggregate.scala
#	plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala

* Resolve backport conflicts

* Do not make MixedVec extend AutoCloneType

It is a binary incompatible change that can wait for 3.6.

* Waive MiMa false positives

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