Port semantic_index to gpui2

Co-Authored-By: Julia Risley <julia@zed.dev>

crates/semantic_index2/src/semantic_index_settings.rs

@@ -0,0 +1,28 @@
+use anyhow;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use settings::Settings;
+
+#[derive(Deserialize, Debug)]
+pub struct SemanticIndexSettings {
+    pub enabled: bool,
+}
+
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
+pub struct SemanticIndexSettingsContent {
+    pub enabled: Option<bool>,
+}
+
+impl Settings for SemanticIndexSettings {
+    const KEY: Option<&'static str> = Some("semantic_index");
+
+    type FileContent = SemanticIndexSettingsContent;
+
+    fn load(
+        default_value: &Self::FileContent,
+        user_values: &[&Self::FileContent],
+        _: &mut gpui::AppContext,
+    ) -> anyhow::Result<Self> {
+        Self::load_via_json_merge(default_value, user_values)
+    }
+}