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/assistant/src/assistant_panel.rs

@@ -50,11 +50,11 @@ use indexed_docs::IndexedDocsStore;
 use language::{
     language_settings::SoftWrap, BufferSnapshot, LanguageRegistry, LspAdapterDelegate, ToOffset,
 };
-use language_model::{
-    provider::cloud::PROVIDER_ID, LanguageModelProvider, LanguageModelProviderId,
-    LanguageModelRegistry, Role,
-};
 use language_model::{LanguageModelImage, LanguageModelToolUse};
+use language_model::{
+    LanguageModelProvider, LanguageModelProviderId, LanguageModelRegistry, Role,
+    ZED_CLOUD_PROVIDER_ID,
+};
 use multi_buffer::MultiBufferRow;
 use picker::{Picker, PickerDelegate};
 use project::lsp_store::LocalLspAdapterDelegate;
@@ -664,7 +664,7 @@ impl AssistantPanel {
         // If we're signed out and don't have a provider configured, or we're signed-out AND Zed.dev is
         // the provider, we want to show a nudge to sign in.
         let show_zed_ai_notice = client_status.is_signed_out()
-            && active_provider.map_or(true, |provider| provider.id().0 == PROVIDER_ID);
+            && active_provider.map_or(true, |provider| provider.id().0 == ZED_CLOUD_PROVIDER_ID);
 
         self.show_zed_ai_notice = show_zed_ai_notice;
         cx.notify();