Add support for Vercel as a language model provider (#33292)

Vercel v0 is an OpenAI-compatible model, so this is mostly a dupe of the
OpenAI provider files with some adaptations for v0, including going
ahead and using the custom endpoint for the API URL field.

Release Notes:

- Added support for Vercel as a language model provider.

crates/language_models/src/language_models.rs

@@ -20,6 +20,7 @@ use crate::provider::mistral::MistralLanguageModelProvider;
 use crate::provider::ollama::OllamaLanguageModelProvider;
 use crate::provider::open_ai::OpenAiLanguageModelProvider;
 use crate::provider::open_router::OpenRouterLanguageModelProvider;
+use crate::provider::vercel::VercelLanguageModelProvider;
 pub use crate::settings::*;
 
 pub fn init(user_store: Entity<UserStore>, client: Arc<Client>, fs: Arc<dyn Fs>, cx: &mut App) {
@@ -77,5 +78,9 @@ fn register_language_model_providers(
         OpenRouterLanguageModelProvider::new(client.http_client(), cx),
         cx,
     );
+    registry.register_provider(
+        VercelLanguageModelProvider::new(client.http_client(), cx),
+        cx,
+    );
     registry.register_provider(CopilotChatLanguageModelProvider::new(cx), cx);
 }