git: Intercept signing prompt from GPG when committing (#34096)

Closes #30111 

- [x] basic implementation
- [x] implementation for remote projects
- [x] surface error output from GPG if signing fails
- [ ] ~~Windows~~

Release Notes:

- git: Passphrase prompts from GPG to unlock commit signing keys are now
shown in Zed.

crates/fs/src/fake_git_repo.rs

@@ -375,8 +375,10 @@ impl GitRepository for FakeGitRepository {
         _message: gpui::SharedString,
         _name_and_email: Option<(gpui::SharedString, gpui::SharedString)>,
         _options: CommitOptions,
+        _ask_pass: AskPassDelegate,
         _env: Arc<HashMap<String, String>>,
-    ) -> BoxFuture<'_, Result<()>> {
+        _cx: AsyncApp,
+    ) -> BoxFuture<'static, Result<()>> {
         unimplemented!()
     }