Migrate to annotate-snippets

annotate-snippets is a library version of rustc's diagnostic report renderer.

By migrating cargo to use it,

• we make them more consistent
• we have more features (coloring trailing notes/help, snippet rendering, etc)
• prepare for moving some of our diagnostics to be lints

Tasks

• #15928
• Clean up multi-line Shell::notes
  • #15942
  • #15943
• Migrate Shell::note to use print_report (#15945)
• Clean up multi-line or multi-part Shell::warns (excluding util/toml/mod.rs warnings)
  • #16035
• Somehow handle util/toml/mod.rs warnings, either create a custom diagnostic type or move the warnings to a lint phase
• Migrate Shell::warn to use print_report (#15917)
• Switch anyhow::Error to a custom error type
• Cleanup multi-line errors
• Migrate error rendering (src/cargo/lib.rs) to print_report (#15922)

Notes:

• We use https://rustc-dev-guide.rust-lang.org/diagnostics.html as our style guide
• Prefer secondary_title over primary_title for now. We can re-evaluate a switch to primary_title later, see https://github.com/rust-lang/cargo/pull/16065#issuecomment-3378611734

Start with the remaining checklist items for Shell::warn, util/toml/mod.rs warnings, anyhow::Error, and error rendering in src/cargo/lib.rs. Read the Rust diagnostics style guide and existing print_report migrations first. Done means the remaining diagnostic paths are migrated consistently, with the listed warning and error cases handled.