Add Select APIs for Hierarchy package (#2210)

* Add Hierarchy trait

* Add Hierarchy trait

* Add Hierarchy scaladoc

* Add license

* Add isA and tests

* Add back isA

* Add new Select APIs for hierarchy package

* Update scaladoc

* Write outlines for tests

* Add tests and fixes to new Select functions

* Make calculate via lazy val

* Apply suggestions from code review

Co-authored-by: Megan Wachs <megan@sifive.com>

* Apply suggestions from code review

Co-authored-by: Megan Wachs <megan@sifive.com>

* Clean up scaladoc

* Add shouldNot compile

* Apply suggestions from code review

Co-authored-by: Megan Wachs <megan@sifive.com>

* Bugfix all funcs should analyze root too

* Add mdoc, bugfix toDefinition

* Make func private, add scaladoc

* Update src/test/scala/chiselTests/experimental/hierarchy/InstanceSpec.scala

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

* Made protected vals private

* Apply suggestions from code review

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

* Address code review comments

* Added additional null check

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