Adds generation of `Bundle#elements` method to the chores done by the `BundleComponent`

For each `Bundle` find the relevant visible Chisel field members and construct a
hard-coded list of the elements and their types and implement as `_elementsImpl`
There is more clean-up to do, but this will record the state of various debugging information

Remaining problems are fields introduced to the bundle from inheritance
This commit contains a Main In HasDemoBundle for development purposes