feat: Add getTextContent method to retrieve message text content

Signed-off-by: liugddx <[email protected]>

Author: liugddx

spring-ai-model/src/main/java/org/springframework/ai/chat/messages/AbstractMessage.java

@@ -108,6 +108,15 @@ public String getText() {
 		return this.textContent;
 	}
 
+	/**
+	 * Get the text content of the message.
+	 * @return the text content of the message
+	 */
+	@Nullable
+	public String getTextContent() {
+		return this.textContent;
+	}
+
 	/**
 	 * Get the metadata of the message.
 	 * @return the metadata of the message