Handle DataBufferLimitException as HTTP 413 responses

Prior to this commit, `DataBufferLimitException` would be thrown by
codecs when the request body was too large for the configured buffer
limit. This exception would not be handled by the web infrastructure and
would result in an HTTP 500 server error.

This commit introduces a new `PayloadTooLargeException` type that will
result in an HTTP 413 "Payload too large" response status.

Closes gh-32558

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MessageReaderArgumentResolverTests.java

@@ -52,6 +52,7 @@ import org.springframework.validation.annotation.Validated;
 import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.reactive.BindingContext;
+import org.springframework.web.server.PayloadTooLargeException;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.ServerWebInputException;
 import org.springframework.web.server.UnsupportedMediaTypeStatusException;
@@ -112,6 +113,24 @@ class MessageReaderArgumentResolverTests {
 		StepVerifier.create(result).expectError(ServerWebInputException.class).verify();
 	}
 
+	@Test @SuppressWarnings("unchecked")
+	public void tooLargeBody() {
+		StringBuilder bodyBuilder = new StringBuilder();
+		while (bodyBuilder.toString().getBytes().length < 256 * 1024) {
+			bodyBuilder.append("The default maximum input length is 256kb.");
+		}
+		String body = "{\"bar\":\"BARBAR\",\"foo\":\"" + bodyBuilder + "\"}";
+
+		MockServerHttpRequest request = post("/path").contentType(MediaType.APPLICATION_JSON).body(body);
+		ServerWebExchange exchange = MockServerWebExchange.from(request);
+		ResolvableType type = forClassWithGenerics(Mono.class, TestBean.class);
+		MethodParameter param = this.testMethod.arg(type);
+		Mono<TestBean> result = (Mono<TestBean>) this.resolver.readBody(
+				param, true, this.bindingContext, exchange).block();
+
+		StepVerifier.create(result).expectError(PayloadTooLargeException.class).verify();
+	}
+
 	@Test
 	void monoTestBean() {
 		String body = "{\"bar\":\"BARBAR\",\"foo\":\"FOOFOO\"}";