Document DataTransferItem (#151442)

This adds missing documentation to the `DataTransferItem` api type

src/vscode-dts/vscode.d.ts

@@ -10058,14 +10058,27 @@ declare module 'vscode' {
 	}
 
 	/**
-	 * A class for encapsulating data transferred during a drag and drop event.
-	 *
-	 * You can use the `value` of the `DataTransferItem` to get back the object you put into it
-	 * so long as the extension that created the `DataTransferItem` runs in the same extension host.
+	 * Encapsulates data transferred during drag and drop operations.
 	 */
 	export class DataTransferItem {
+		/**
+		 * Get a string representation of this item.
+		 *
+		 * If {@linkcode DataTransferItem.value} is an object, this returns the result of json stringifying {@linkcode DataTransferItem.value} value.
+		 */
 		asString(): Thenable<string>;
+
+		/**
+		 * Custom data stored on this item.
+		 *
+		 * You can use `value` to share data across operations. The original object can be retrieved so long as the extension that
+		 * created the `DataTransferItem` runs in the same extension host.
+		 */
 		readonly value: any;
+
+		/**
+		 * @param value Custom data stored on this item. Can be retrieved using {@linkcode DataTransferItem.value}.
+		 */
 		constructor(value: any);
 	}