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/google_ai/src/google_ai.rs

@@ -493,7 +493,7 @@ pub enum Model {
 
 impl Model {
     pub fn default_fast() -> Model {
-        Model::Gemini15Flash
+        Model::Gemini20Flash
     }
 
     pub fn id(&self) -> &str {