Update default models to newer versions (#31415)

Follow up to: https://github.com/zed-industries/zed/pull/31209
Changes default models across multiple providers:
- Zed.dev Default Models in settings: claude-3-7-sonnet-latest →
claude-4-sonnet-latest
- Bedrock Default Model: Claude 3.5 Sonnet v2 → Claude Sonnet 4
- Google AI Default Fast Model: Gemini 1.5 Flash → Gemini 2.0 Flash

Release Notes:

- N/A

crates/assistant_settings/src/assistant_settings.rs

@@ -1018,7 +1018,7 @@ mod tests {
                 AssistantSettings::get_global(cx).default_model,
                 LanguageModelSelection {
                     provider: "zed.dev".into(),
-                    model: "claude-3-7-sonnet-latest".into(),
+                    model: "claude-4-sonnet".into(),
                 }
             );
         });