Draft: refactor cli with annotate-snippets

[suaviloquence]

Opening this PR not to merge immediately (or even ever) but to show what we could do with annotate-snippets and get feedback on the CLI design (to be more rustc/clippy-like).

Screenshots:

cargo semver-checks --baseline-root test_crates/function_const_removed/old --manifest-path test_crates/function_const_removed/new -Z unstable-options --witness-hints

old

new

when file is not available for span

on manifest_tests/workspace_overrides test crate (warnings + errors)

old

new

On compatibility with clippy/rustc:

This is mostly just a port of our current failure printing to use annotate-snippets (and adding printing the one-line span snippet).

clippy/rustc linters show generally less information per lint, and don't group instances of lints occurring by lint type. We group all lint results and print lots of info for each lint (description, ref link, info link) as well as per-result error info.

sample clippy/rustc lints

I don't know if we actually want parity with rustc in this regard, though.