New revision of the Assistant Panel (#10870)

This is a crate only addition of a new version of the AssistantPanel.
We'll be putting this behind a feature flag while we iron out the new
experience.

Release Notes:

- N/A

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Conrad Irwin <conrad@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Antonio Scandurra <antonio@zed.dev>
Co-authored-by: Nate Butler <nate@zed.dev>
Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Max <max@zed.dev>

crates/assistant/src/assistant.rs

@@ -128,6 +128,8 @@ impl LanguageModelRequestMessage {
                 Role::System => proto::LanguageModelRole::LanguageModelSystem,
             } as i32,
             content: self.content.clone(),
+            tool_calls: Vec::new(),
+            tool_call_id: None,
         }
     }
 }
@@ -147,6 +149,8 @@ impl LanguageModelRequest {
             messages: self.messages.iter().map(|m| m.to_proto()).collect(),
             stop: self.stop.clone(),
             temperature: self.temperature,
+            tool_choice: None,
+            tools: Vec::new(),
         }
     }
 }