Make the ReadOnlyArrayMap extend AbstractMap for equals/hashcode implementation (#2963)

* Make the ReadOnlyArrayMap extend AbstractMap for equals/hashcode implementation

* formatting

* use guava's EqualsTester to save a few lines

* remove redundant hashcode verifications

* add an empty map to the equals test

api/all/src/main/java/io/opentelemetry/api/internal/ReadOnlyArrayMap.java

@@ -32,7 +32,7 @@ import java.util.Set;
 
 /** A read-only view of an array of key-value pairs. */
 @SuppressWarnings("unchecked")
-public final class ReadOnlyArrayMap<K, V> implements Map<K, V> {
+public final class ReadOnlyArrayMap<K, V> extends AbstractMap<K, V> {
 
   /** Returns a read-only view of the given {@code array}. */
   public static <K, V> Map<K, V> wrap(List<Object> array) {

api/all/src/test/java/io/opentelemetry/api/internal/ReadOnlyArrayMapTest.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.api.internal;
+
+import com.google.common.testing.EqualsTester;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+
+class ReadOnlyArrayMapTest {
+
+  @Test
+  void equalsHashCode() {
+    Map<String, String> one = ReadOnlyArrayMap.wrap(Arrays.asList("a", "b"));
+    Map<String, String> two = ReadOnlyArrayMap.wrap(Arrays.asList("a", "b"));
+    Map<String, String> three = ReadOnlyArrayMap.wrap(Arrays.asList("c", "d"));
+    Map<String, String> empty = ReadOnlyArrayMap.wrap(Collections.emptyList());
+    new EqualsTester()
+        .addEqualityGroup(one, two)
+        .addEqualityGroup(three)
+        .addEqualityGroup(empty, empty)
+        .testEquals();
+  }
+}