Add Cargo.toml context to exported-private-dependencies lints

[epage]

Problem

Right now the lint just says

warning: trait `FooTrait` from private dependency 'foo' in public interface
  --> src/lib.rs:25:1
   |
25 | pub fn use_foo_trait<F: foo::FooTrait>(_: Local) {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

rustc has no knowledge of Cargo.toml to provide additional context

Proposed Solution

Build on #13095 and #12235 to inject a note in the lint to highlight the dependency in Cargo.toml, saying the dependency is private

Notes

No response