Make auto-configured Brave Tracer more compliant with OTel tracer

By default we will not support joined spans and the trace ID will
be 128-bit.

See gh-32615

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/BraveAutoConfiguration.java

@@ -92,8 +92,9 @@ public class BraveAutoConfiguration {
 			List<TracingCustomizer> tracingCustomizers, CurrentTraceContext currentTraceContext,
 			Factory propagationFactory, Sampler sampler) {
 		String applicationName = environment.getProperty("spring.application.name", DEFAULT_APPLICATION_NAME);
-		Builder builder = Tracing.newBuilder().currentTraceContext(currentTraceContext)
+		Builder builder = Tracing.newBuilder().currentTraceContext(currentTraceContext).traceId128Bit(true)
-				.propagationFactory(propagationFactory).sampler(sampler).localServiceName(applicationName);
+				.supportsJoin(false).propagationFactory(propagationFactory).sampler(sampler)
+				.localServiceName(applicationName);
 		for (SpanHandler spanHandler : spanHandlers) {
 			builder.addSpanHandler(spanHandler);
 		}

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/BraveAutoConfigurationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
+import brave.Span;
 import brave.Tracer;
 import brave.Tracing;
 import brave.baggage.BaggagePropagation;
@@ -211,6 +212,27 @@ class BraveAutoConfigurationTests {
 				.run((context) -> assertThat(context).hasBean("mdcCorrelationScopeDecoratorBuilder"));
 	}
 
+	@Test
+	void shouldHave128BitTraceId() {
+		this.contextRunner.run((context) -> {
+			Tracing tracing = context.getBean(Tracing.class);
+			Span span = tracing.tracer().nextSpan();
+			assertThat(span.context().traceIdString()).hasSize(32);
+		});
+	}
+
+	@Test
+	void shouldNotSupportJoinedSpans() {
+		this.contextRunner.run((context) -> {
+			Tracing tracing = context.getBean(Tracing.class);
+			Span parentSpan = tracing.tracer().nextSpan();
+			Span childSpan = tracing.tracer().joinSpan(parentSpan.context());
+			assertThat(parentSpan.context().traceIdString()).isEqualTo(childSpan.context().traceIdString());
+			assertThat(parentSpan.context().spanIdString()).isEqualTo(childSpan.context().parentIdString());
+			assertThat(parentSpan.context().spanIdString()).isNotEqualTo(childSpan.context().spanIdString());
+		});
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	private static class CustomConfiguration {