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/language_model/src/language_model.rs

@@ -54,6 +54,10 @@ pub struct LanguageModelCacheConfiguration {
 pub trait LanguageModel: Send + Sync {
     fn id(&self) -> LanguageModelId;
     fn name(&self) -> LanguageModelName;
+    /// If None, falls back to [LanguageModelProvider::icon]
+    fn icon(&self) -> Option<IconName> {
+        None
+    }
     fn provider_id(&self) -> LanguageModelProviderId;
     fn provider_name(&self) -> LanguageModelProviderName;
     fn telemetry_id(&self) -> String;