feat: diagnostics for stale dependencies

[mhuisi]

Sends a diagnostic informing the user to run Restart File when a file dependency is saved.

Based on #3014 because this feature was easier to implement with the new architecture.

ToDo:

• [x] Adjust vscode-lean4 to display a notification when this diagnostic appears in a non-annoying way (https://github.com/leanprover/vscode-lean4/pull/393)
• [x] Use a file watcher to identify changes to files not tracked by VS Code
• [ ] Rebase onto master when #3014 is merged

[leanprover-community-mathlib4-bot]

Mathlib CI status (docs):

• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. (2024-02-02 17:37:28)
• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase ea665de4536061cb8b6a1b32f5b69f09d50ac335 --onto 8b8e001794e6a8b481d37f24fa77bb07797682a1. (2024-02-23 13:24:10)
• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 68eaf33e86689e3f303d38e2f071b5e8b7fd172f --onto 317adf42e92a4dbe07295bc1f0429b61bb8079fe. (2024-03-14 16:35:12)
• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 795e332fb37729f013c9a66b211fd45e5c90a1f9 --onto 317adf42e92a4dbe07295bc1f0429b61bb8079fe. (2024-03-14 17:23:08)
• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 14654d802d8950f75a6a2113a7d6288dd2f6cb19 --onto 173b95696129f5efeac9d2cd5a83a724c48cf7ae. (2024-03-15 11:16:19)
• ❗ Std/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase e47d8ca5cdfc1bf8a31adf14814a55511fe922ff --onto 173b95696129f5efeac9d2cd5a83a724c48cf7ae. (2024-03-15 13:43:57)