Coverage option that does not require cbmc-viewer

[adpaco-aws]

Requested feature: In the past, Kani has relied on cbmc-viewer to generate coverage reports. This requires Kani to make additional calls to cbmc with the --cover flag, then cbmc-viewer to essentially perform postprocessing on that output. Unfortunately, the information reported by cbmc-viewer isn't tested thoroughly (see #2048). But actually, Kani already has the tools required for generating coverage-oriented information. Having an option that enables this would allow us to remove the cbmc-viewer dependency and have end-to-end testing for coverage information.

Use case: Coverage reports.
Link to relevant documentation (Rust reference, Nomicon, RFC): N/A

[jaisnan]

Should we tag our PR for this issue?