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/bedrock/src/models.rs

@@ -15,6 +15,7 @@ pub enum BedrockModelMode {
 #[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq, EnumIter)]
 pub enum Model {
     // Anthropic models (already included)
+    #[default]
     #[serde(rename = "claude-sonnet-4", alias = "claude-sonnet-4-latest")]
     ClaudeSonnet4,
     #[serde(
@@ -29,7 +30,6 @@ pub enum Model {
         alias = "claude-opus-4-thinking-latest"
     )]
     ClaudeOpus4Thinking,
-    #[default]
     #[serde(rename = "claude-3-5-sonnet-v2", alias = "claude-3-5-sonnet-latest")]
     Claude3_5SonnetV2,
     #[serde(rename = "claude-3-7-sonnet", alias = "claude-3-7-sonnet-latest")]