fix(appsec/jetty): use Request bytecode discriminator for jetty-appsec-11.0

Replace the JAKARTA_PART_REFERENCE classpath check with a _dispatcherType
field descriptor check on Request.class bytecode, mirroring the approach
already used by jetty-appsec-9.4. The classpath check passes on any
Jetty 9.4/10 app that has jakarta.servlet-api as a dependency, causing
double-instrumentation of extractContentParameters. The bytecode check is
authoritative: in Jetty 11+ Request.class carries _dispatcherType as
Ljakarta/servlet/DispatcherType;, while 9.4/10 carry the javax descriptor.

Author: jandro996

dd-java-agent/instrumentation/jetty/jetty-appsec/jetty-appsec-11.0/src/main/java/datadog/trace/instrumentation/jetty11/RequestExtractContentParametersInstrumentation.java

@@ -61,21 +61,22 @@ public void methodAdvice(MethodTransformer transformer) {
   // Discriminates Jetty 11.0.x ([11.0, 12.0)):
   //  - _contentParameters + extractContentParameters(void) exist in 11.x (excludes Jetty 12
   //    where org.eclipse.jetty.server.Request was removed)
-  //  - jakarta.servlet.http.Part exists in 11.x classpath (excludes 9.4–10.x which use javax)
+  //  - _dispatcherType: Ljakarta/servlet/DispatcherType; in the Request bytecode (excludes
+  //    Jetty 9.4–10.x where the field descriptor is Ljavax/servlet/DispatcherType;). This check
+  //    is tied to Request.class bytecode, NOT just classpath presence, so it works even when both
+  //    javax.servlet and jakarta.servlet are on the classpath simultaneously.
   // NOTE: _multiParts changes type at 11.0.10 (MultiPartFormInputStream → MultiParts); both
   // are handled transparently because GetFilenamesAdvice reads it with typing=DYNAMIC.
   private static final Reference REQUEST_REFERENCE =
       new Reference.Builder("org.eclipse.jetty.server.Request")
           .withMethod(new String[0], 0, "extractContentParameters", "V")
           .withField(new String[0], 0, "_contentParameters", MULTI_MAP_INTERNAL_NAME)
+          .withField(new String[0], 0, "_dispatcherType", "Ljakarta/servlet/DispatcherType;")
           .build();
 
-  private static final Reference JAKARTA_PART_REFERENCE =
-      new Reference.Builder("jakarta.servlet.http.Part").build();
-
   @Override
   public Reference[] additionalMuzzleReferences() {
-    return new Reference[] {REQUEST_REFERENCE, JAKARTA_PART_REFERENCE};
+    return new Reference[] {REQUEST_REFERENCE};
   }
 
   @RequiresRequestContext(RequestContextSlot.APPSEC)