assistant: Add foundation for receiving tool uses from Anthropic models (#17170)

This PR updates the Assistant with support for receiving tool uses from
Anthropic models and capturing them as text in the context editor.

This is just laying the foundation for tool use. We don't yet fulfill
the tool uses yet, or define any tools for the model to use.

Here's an example of what it looks like using the example `get_weather`
tool from the Anthropic docs:

<img width="644" alt="Screenshot 2024-08-30 at 1 51 13 PM"
src="https://github.com/user-attachments/assets/3614f953-0689-423c-8955-b146729ea638">

Release Notes:

- N/A

crates/assistant/src/context.rs

@@ -2048,7 +2048,8 @@ impl Context {
 
         LanguageModelRequest {
             messages: request_messages,
-            stop: vec![],
+            tools: Vec::new(),
+            stop: Vec::new(),
             temperature: 1.0,
         }
     }
@@ -2398,7 +2399,8 @@ impl Context {
                 }));
             let request = LanguageModelRequest {
                 messages: messages.collect(),
-                stop: vec![],
+                tools: Vec::new(),
+                stop: Vec::new(),
                 temperature: 1.0,
             };