fix(appsec/jetty): replace bytecode injection in jetty-appsec-8.1.3 with exit-advice

Replace the brittle GetPartsMethodVisitor ASM bytecode injection (intercepting
MultiMap.add() calls inside getParts()) with a clean ByteBuddy exit-advice approach:

- Remove ParameterCollector, GetPartsAdvice, GetPartsVisitorWrapper, RequestClassVisitor,
  and GetPartsMethodVisitor; drop HasTypeAdvice from the instrumentation module.
- Add PartHelper with extractFormFields() (reads InputStream per part) and
  extractFilenames() (parses Content-Disposition manually, since
  Part.getSubmittedFileName() is Servlet 3.1+ and not available in Jetty 8.x).
- Add GetFilenamesAdvice (@RequiresRequestContext / @ActiveRequestContext) on
  getParts():Collection that fires requestBodyProcessed() with form fields and
  requestFilesFilenames() with upload filenames. Uses CallDepthThreadLocalMap to
  guard against reentrant calls.
- Jetty8LatestDepForkedTest: set testBodyFilenamesCalledOnce() and
  testBodyFilenamesCalledOnceCombined() to false because Jetty 8.x has no
  _multiParts / _contentParameters field guards to suppress duplicate firings.

Author: jandro996

dd-java-agent/instrumentation/jetty/jetty-appsec/jetty-appsec-8.1.3/src/main/java/datadog/trace/instrumentation/jetty8/ParameterCollector.java

@@ -0,0 +1,110 @@
+package datadog.trace.instrumentation.jetty8;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import javax.servlet.http.Part;
+
+/**
+ * Helper for extracting filenames and form-field values from Servlet 3.0 {@link Part} objects.
+ *
+ * <p>{@code Part.getSubmittedFileName()} was added in Servlet 3.1 (Jetty 9.1+); for Jetty 8.x we
+ * must parse the {@code Content-Disposition} header manually.
+ */
+public class PartHelper {
+
+  private PartHelper() {}
+
+  /**
+   * Returns filenames found in {@code parts} by parsing each part's {@code Content-Disposition}
+   * header for a {@code filename=} parameter.
+   */
+  public static List<String> extractFilenames(Collection<?> parts) {
+    if (parts == null || parts.isEmpty()) {
+      return Collections.emptyList();
+    }
+    List<String> filenames = new ArrayList<>();
+    for (Object obj : parts) {
+      String filename = filenameFromPart((Part) obj);
+      if (filename != null && !filename.isEmpty()) {
+        filenames.add(filename);
+      }
+    }
+    return filenames;
+  }
+
+  /**
+   * Returns a name→values map of form-field parts (those without a {@code filename=} parameter).
+   * File-upload parts are skipped to avoid reading potentially large content.
+   */
+  public static Map<String, List<String>> extractFormFields(Collection<?> parts) {
+    if (parts == null || parts.isEmpty()) {
+      return Collections.emptyMap();
+    }
+    Map<String, List<String>> result = new LinkedHashMap<>();
+    for (Object obj : parts) {
+      Part part = (Part) obj;
+      if (filenameFromPart(part) != null) {
+        continue; // file-upload part — skip
+      }
+      String name = part.getName();
+      if (name == null) {
+        continue;
+      }
+      String value = readPartContent(part);
+      if (value == null) {
+        continue;
+      }
+      List<String> values = result.get(name);
+      if (values == null) {
+        values = new ArrayList<>();
+        result.put(name, values);
+      }
+      values.add(value);
+    }
+    return result;
+  }
+
+  /**
+   * Extracts the {@code filename} value from a {@code Content-Disposition} header, or {@code null}
+   * if the part has no filename (i.e. it is a plain form field).
+   */
+  static String filenameFromPart(Part part) {
+    String cd = part.getHeader("Content-Disposition");
+    if (cd == null) {
+      return null;
+    }
+    for (String token : cd.split(";")) {
+      token = token.trim();
+      if (token.startsWith("filename=")) {
+        String name = token.substring("filename=".length()).trim();
+        if (name.length() >= 2 && name.charAt(0) == '"' && name.charAt(name.length() - 1) == '"') {
+          name = name.substring(1, name.length() - 1);
+        }
+        return name.isEmpty() ? null : name;
+      }
+    }
+    return null;
+  }
+
+  private static String readPartContent(Part part) {
+    try {
+      InputStream is = part.getInputStream();
+      ByteArrayOutputStream baos = new ByteArrayOutputStream();
+      byte[] buf = new byte[4096];
+      int read;
+      while ((read = is.read(buf)) != -1) {
+        baos.write(buf, 0, read);
+      }
+      return baos.toString("UTF-8");
+    } catch (IOException e) {
+      return null;
+    }
+  }
+}