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/terminal_inline_assistant.rs

@@ -17,9 +17,9 @@ use gpui::{
 };
 use language::Buffer;
 use language_model::{
-    logging::report_assistant_event, LanguageModelRegistry, LanguageModelRequest,
-    LanguageModelRequestMessage, Role,
+    LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, Role,
 };
+use language_models::report_assistant_event;
 use settings::Settings;
 use std::{
     cmp,