incremental: migrate diagnostics

[davidtwco]

• Apply the diagnostic migration lints to more functions on Session, namely: span_warn, span_warn_with_code, warn note_without_error, span_note_without_error, struct_note_without_error.
• Add impls of IntoDiagnosticArg for std::io::Error, std::path::Path and std::path::PathBuf.
• Migrate the rustc_incremental crate's diagnostics to translatable diagnostic structs.

r? @compiler-errors
cc #100717