http-api: rebased to have multimap use a linkedhashset instead of hashset when getting keys to remove non-deterministic behaviors

Author: lawrencewang49

servicetalk-http-api/src/main/java/io/servicetalk/http/api/MultiMap.java

@@ -18,6 +18,7 @@
 import java.util.Arrays;
 import java.util.ConcurrentModificationException;
 import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -144,7 +145,7 @@ final Set<? extends K> getKeys() {
             return emptySet();
         }
         // Overall iteration order does not need to be preserved.
-        final Set<K> names = new HashSet<>((int) (size() / .75), .75f);
+        final Set<K> names = new LinkedHashSet<>((int) (size() / .75), .75f);
         BucketHead<K, V> bucketHead = lastBucketHead;
         while (bucketHead != null) {
             MultiMapEntry<K, V> e = bucketHead.entry;

servicetalk-http-api/src/test/java/io/servicetalk/http/api/AbstractHttpHeadersTest.java

@@ -434,6 +434,9 @@ void headersWithSameNamesAndValuesShouldBeEquivalent() {
         assertEquals(headers2, headers1);
         assertEquals(headers1, headers1);
         assertEquals(headers2, headers2);
+        assertEquals(headers1.hashCode(), headers2.hashCode());
+        assertEquals(headers1.hashCode(), headers1.hashCode());
+        assertEquals(headers2.hashCode(), headers2.hashCode());
     }
 
     @Test