Print RuntimeException raised by StructuredLogFormatter::format to system err

Before this commit, runtime exception is swallowed silently.

For example, if two `StructuredLoggingJsonMembersCustomizer` add same key, exception is printed now:
```
Exception in thread "main" java.lang.IllegalStateException: The name 'test' has already been written
	at org.springframework.util.Assert.state(Assert.java:101)
	at org.springframework.boot.json.JsonValueWriter.writePair(JsonValueWriter.java:228)
	at org.springframework.boot.json.JsonValueWriter.write(JsonValueWriter.java:83)
	at org.springframework.boot.json.JsonWriter$Member.write(JsonWriter.java:650)
	at org.springframework.boot.json.JsonWriter$Members.write(JsonWriter.java:339)
```

Author: quaff

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/structured/JsonWriterStructuredLogFormatter.java

@@ -29,6 +29,7 @@
  *
  * @param <E> the log event type
  * @author Phillip Webb
+ * @author Yanming Zhou
  * @since 3.4.0
  */
 public abstract class JsonWriterStructuredLogFormatter<E> implements StructuredLogFormatter<E> {
@@ -68,12 +69,26 @@ protected JsonWriterStructuredLogFormatter(JsonWriter<E> jsonWriter) {
 
 	@Override
 	public String format(E event) {
-		return this.jsonWriter.writeToString(event);
+		try {
+			return this.jsonWriter.writeToString(event);
+		}
+		catch(RuntimeException ex) {
+			// exception can not be logged due to "Chicken-and-egg" problem
+			ex.printStackTrace(System.err);
+			throw ex;
+		}
 	}
 
 	@Override
 	public byte[] formatAsBytes(E event, Charset charset) {
-		return this.jsonWriter.write(event).toByteArray(charset);
+		try {
+			return this.jsonWriter.write(event).toByteArray(charset);
+		}
+		catch(RuntimeException ex) {
+			// exception can not be logged due to "Chicken-and-egg" problem
+			ex.printStackTrace(System.err);
+			throw ex;
+		}
 	}
 
 }