Add language_models crate to house language model providers (#20945)

This PR adds a new `language_models` crate to house the various language
model providers.

By extracting the provider definitions out of `language_model`, we're
able to remove `language_model`'s dependency on `editor`, which improves
incremental compilation when changing `editor`.

Release Notes:

- N/A

crates/zed/Cargo.toml

@@ -61,6 +61,7 @@ install_cli.workspace = true
 journal.workspace = true
 language.workspace = true
 language_model.workspace = true
+language_models.workspace = true
 language_selector.workspace = true
 language_tools.workspace = true
 languages = { workspace = true, features = ["load-grammars"] }

crates/zed/src/main.rs

@@ -387,7 +387,8 @@ fn main() {
             cx,
         );
         supermaven::init(app_state.client.clone(), cx);
-        language_model::init(
+        language_model::init(cx);
+        language_models::init(
             app_state.user_store.clone(),
             app_state.client.clone(),
             app_state.fs.clone(),

crates/zed/src/zed.rs

@@ -3504,7 +3504,8 @@ mod tests {
                 app_state.client.http_client().clone(),
                 cx,
             );
-            language_model::init(
+            language_model::init(cx);
+            language_models::init(
                 app_state.user_store.clone(),
                 app_state.client.clone(),
                 app_state.fs.clone(),