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

docs/src/configuring-zed.md

@@ -3287,11 +3287,11 @@ Run the `theme selector: toggle` action in the command palette to see a current
   "default_view": "thread",
   "default_model": {
     "provider": "zed.dev",
-    "model": "claude-3-7-sonnet-latest"
+    "model": "claude-4-sonnet"
   },
   "editor_model": {
     "provider": "zed.dev",
-    "model": "claude-3-7-sonnet-latest"
+    "model": "claude-4-sonnet"
   },
   "single_file_review": true,
 }