Eliminate Java 9+ dependency for UP (elastic#4286)

* Eliminate Java 9+ dependency for UP

* add changelog entry

Author: jackshirazi

CHANGELOG.next-release.md

@@ -9,7 +9,7 @@ This file contains all changes which are not released yet.
 
 # Fixes
 <!--FIXES-START-->
-
+Prevent Universal Profiling integration crashing agent on startup when run on Java 8 - [#4286](https://github.com/elastic/apm-agent-java/pull/4286)
 <!--FIXES-END-->
 # Features and enhancements
 <!--ENHANCEMENTS-START-->

apm-agent-core/src/main/java/co/elastic/apm/agent/universalprofiling/ProfilerSharedMemoryWriter.java

@@ -25,6 +25,7 @@
 import co.elastic.otel.UniversalProfilingCorrelation;
 
 import javax.annotation.Nullable;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.charset.StandardCharsets;
@@ -47,7 +48,8 @@ public class ProfilerSharedMemoryWriter {
     static ByteBuffer generateProcessCorrelationStorage(String serviceName, @Nullable String environment, String socketFilePath) {
         ByteBuffer buffer = ByteBuffer.allocateDirect(4096);
         buffer.order(ByteOrder.nativeOrder());
-        buffer.position(0);
+        //To make it java 8 compatible regardless of how it's compiled, need to explicitly use Buffer.position(int)
+        ((Buffer) buffer).position(0);
 
         buffer.putChar((char) 1); // layout-minor-version
         writeUtf8Str(buffer, serviceName);