Feature request - action to add deprecation to item

I'd like to improve the experience of incrementally migrating bits of a codebase. A workflow I'll use is:

• write the new implementation
• mark the old implementation as deprecated and add '#[allow(deprecated)] to all of the uses
• migrate each use incrementally

This allows the migration process to be split up into multiple, smaller PRs, which are easier to review, without breaking the build in between.

However, in some cases, there are hundreds/thousands of uses, and it takes a long time to go through and manually add #[allow(deprecated)] to the old usages.

I'd be keen to see a code action for something like: "deprecate and whitelist usages" on items. For example:

fn old_function()  {
  println!("old implementation")
}

fn main() {
  old_function();
}

would become

#[deprecated]
fn old_function()  {
  println!("old implementation")
}

fn main() {
  #[allow(deprecated)]
  old_function();
}

Does this sound like something useful? If so I'd be happy to work on a PR

Start by locating rust-analyzer's existing code-action handling for Rust deprecation diagnostics and item usages. Use the Rust example in the issue as the acceptance case: the action should deprecate the selected item and add #[allow(deprecated)] to its usages, with the resulting code showing the requested migration workflow.