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/log4j2/StructuredLogLayout.java

@@ -43,6 +43,7 @@
  *
  * @author Moritz Halbritter
  * @author Phillip Webb
+ * @author Yanming Zhou
  * @see StructuredLogFormatter
  */
 @Plugin(name = "StructuredLogLayout", category = Node.CATEGORY, elementType = Layout.ELEMENT_TYPE)
@@ -58,12 +59,26 @@ private StructuredLogLayout(Charset charset, StructuredLogFormatter<LogEvent> fo
 
 	@Override
 	public String toSerializable(LogEvent event) {
-		return this.formatter.format(event);
+		try {
+			return this.formatter.format(event);
+		}
+		catch (RuntimeException ex) {
+			// exception can not be logged due to "Chicken-and-egg" problem
+			ex.printStackTrace(System.err);
+			throw ex;
+		}
 	}
 
 	@Override
 	public byte[] toByteArray(LogEvent event) {
-		return this.formatter.formatAsBytes(event, (getCharset() != null) ? getCharset() : StandardCharsets.UTF_8);
+		try {
+			return this.formatter.formatAsBytes(event, (getCharset() != null) ? getCharset() : StandardCharsets.UTF_8);
+		}
+		catch (RuntimeException ex) {
+			// exception can not be logged due to "Chicken-and-egg" problem
+			ex.printStackTrace(System.err);
+			throw ex;
+		}
 	}
 
 	@PluginBuilderFactory

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/StructuredLogEncoder.java

@@ -39,6 +39,7 @@
  *
  * @author Moritz Halbritter
  * @author Phillip Webb
+ * @author Yanming Zhou
  * @since 3.4.0
  * @see StructuredLogFormatter
  */
@@ -124,7 +125,14 @@ public byte[] headerBytes() {
 
 	@Override
 	public byte[] encode(ILoggingEvent event) {
-		return this.formatter.formatAsBytes(event, (this.charset != null) ? this.charset : StandardCharsets.UTF_8);
+		try {
+			return this.formatter.formatAsBytes(event, (this.charset != null) ? this.charset : StandardCharsets.UTF_8);
+		}
+		catch (RuntimeException ex) {
+			// exception can not be logged due to "Chicken-and-egg" problem
+			ex.printStackTrace(System.err);
+			throw ex;
+		}
 	}
 
 	@Override