language_model: Remove dependency on inline_completion_button (#20930)

This PR removes a dependency on the `inline_completion_button` crate
from the `language_model` crate.

We were taking on this dependency solely to call `initiate_sign_in`,
which can easily be moved to the `copilot` crate.

This allows `language_model` to move up in the crate dependency graph.

Release Notes:

- N/A

crates/welcome/Cargo.toml

@@ -17,10 +17,10 @@ test-support = []
 [dependencies]
 anyhow.workspace = true
 client.workspace = true
+copilot.workspace = true
 db.workspace = true
 fuzzy.workspace = true
 gpui.workspace = true
-inline_completion_button.workspace = true
 install_cli.workspace = true
 picker.workspace = true
 project.workspace = true

crates/welcome/src/welcome.rs

@@ -177,7 +177,7 @@ impl Render for WelcomePage {
                                                 this.telemetry.report_app_event(
                                                     "welcome page: sign in to copilot".to_string(),
                                                 );
-                                                inline_completion_button::initiate_sign_in(cx);
+                                                copilot::initiate_sign_in(cx);
                                             }),
                                         ),
                                     )