Bump to Chisel 3.5

[davidbiancolin]

This pulls in all the necessary changes from currently open PRs to complete a bump to Chisel 3.5. For various reasons, some of those earlier PRs cannot pass CI standalone, so it was easiest (for me) to bundle them together.
These PRs include:
Bumping hardfloat (closes #2930)
Removing clonetype (closes #2889)
Removing the old property and updating cover (closes #2890)

Other notes:

• I bumped macro paradise to 2.1.1 so that a published version could be found for scala 2.12.15. We already do this in the mill build, it appears. If that is undesired, can someone point me at a place where it is published and we can update the resolvers?
• I tried to update the mill files. @sequencer how should i test them?

Related issue:

Type of change: other enhancement

Impact: API addition (no impact on existing code)

Development Phase: implementation

Release Notes

Bump to Chisel 3.5.

[sequencer]

Thanks @davidbiancolin! I'll work check this today(maybe 8~10 hours later)

[davidbiancolin]

Thanks @davidbiancolin! I'll work check this today(maybe 8~10 hours later)

Feel free to just push to this branch.

[sequencer]

Finally!

[jackkoenig]

@michael-etzkorn you definitely need the plugin to use the same (at least major) version of Chisel. All Chisel related projects must be in sync on major version, see https://www.chisel-lang.org/chisel3/docs/appendix/versioning.html