Add custom icon for Anthropic hosted models (#16436)

This commit adds a custom icon for Anthropic hosted models.


![CleanShot 2024-08-18 at 15 40
38@2x](https://github.com/user-attachments/assets/d467ccab-9628-4258-89fc-782e0d4a48d4)
![CleanShot 2024-08-18 at 15 40
34@2x](https://github.com/user-attachments/assets/7efaff9c-6a58-47ba-87ea-e0fe0586fedc)


- Adding a new SVG icon for Anthropic hosted models.
  - The new icon is located at: `assets/icons/ai_anthropic_hosted.svg`
- Updating the LanguageModel trait to include an optional icon method
- Implementing the icon method for CloudModel to return the custom icon
for Anthropic hosted models
- Updating the UI components to use the model-specific icon when
available
- Adding a new IconName variant for the Anthropic hosted icon

We should change the non-hosted icon in some small way to distinguish it
from the hosted version. I duplicated the path for now so we can
hopefully add it for the next release.

Release Notes:

- N/A

crates/assistant/src/model_selector.rs

@@ -36,7 +36,7 @@ pub struct ModelPickerDelegate {
 #[derive(Clone)]
 struct ModelInfo {
     model: Arc<dyn LanguageModel>,
-    provider_icon: IconName,
+    icon: IconName,
     availability: LanguageModelAvailability,
     is_selected: bool,
 }
@@ -156,7 +156,7 @@ impl PickerDelegate for ModelPickerDelegate {
                 .selected(selected)
                 .start_slot(
                     div().pr_1().child(
-                        Icon::new(model_info.provider_icon)
+                        Icon::new(model_info.icon)
                             .color(Color::Muted)
                             .size(IconSize::Medium),
                     ),
@@ -261,16 +261,17 @@ impl<T: PopoverTrigger> RenderOnce for ModelSelector<T> {
             .iter()
             .flat_map(|provider| {
                 let provider_id = provider.id();
-                let provider_icon = provider.icon();
+                let icon = provider.icon();
                 let selected_model = selected_model.clone();
                 let selected_provider = selected_provider.clone();
 
                 provider.provided_models(cx).into_iter().map(move |model| {
                     let model = model.clone();
+                    let icon = model.icon().unwrap_or(icon);
 
                     ModelInfo {
                         model: model.clone(),
-                        provider_icon,
+                        icon,
                         availability: model.availability(),
                         is_selected: selected_model.as_ref() == Some(&model.id())
                             && selected_provider.as_ref() == Some(&provider_id),