Fix Array.appendAll() arraycopy type mismatch (#2795)

Internal `Array.appendAll` optimizations sometimes would result in returning arrays of the wrong type.

```java
private interface SomeInterface {
}

enum OneEnum implements SomeInterface {
    A1, A2, A3;
}

enum SecondEnum implements SomeInterface {
    A1, A2, A3;
}

public static void main(String[] args) {
    Array<SomeInterface> empty = Array.empty();
    Array<SomeInterface> copy1 = empty.appendAll(Array.<SomeInterface>of(OneEnum.values()));
    Array<SomeInterface> copy2 = copy1.appendAll(Array.<SomeInterface>of(SecondEnum.values()));
}
```

----
fixes: #2781

vavr/src/main/java/io/vavr/collection/Array.java

@@ -621,7 +621,7 @@ public Array<T> appendAll(Iterable<? extends T> elements) {
         if (source.length == 0) {
             return this;
         } else {
-            final Object[] arr = copyOf(delegate, delegate.length + source.length);
+            final Object[] arr = copyOf(delegate, delegate.length + source.length, Object[].class);
             System.arraycopy(source, 0, arr, delegate.length, source.length);
             return wrap(arr);
         }

vavr/src/test/java/io/vavr/collection/AbstractSeqTest.java

@@ -228,6 +228,16 @@ public void shouldAppendAllNonNilToNonNil() {
         assertThat(actual).isEqualTo(expected);
     }
 
+    @Test
+    public void shouldAppendAllWhenUsedWithTypeHierarchy() {
+        final Seq<SomeInterface> empty = of();
+        final Seq<SomeInterface> all = empty
+          .appendAll(of(OneEnum.values()))
+          .appendAll(of(SecondEnum.values()));
+
+        assertThat(all).isEqualTo(this.<SomeInterface>of(OneEnum.A1, OneEnum.A2, OneEnum.A3, SecondEnum.A1, SecondEnum.A2, SecondEnum.A3));
+    }
+
     @Test
     public void shouldReturnSameSeqWhenEmptyAppendAllEmpty() {
         final Seq<Integer> empty = empty();
@@ -2276,4 +2286,14 @@ public void shouldTestIndexedSeqEndsWithNonIndexedSeq() {
         assertThat(of(1, 2, 3, 4).endsWith(Stream.of(2, 3, 5))).isFalse();
     }
 
+    private interface SomeInterface {
+    }
+
+    enum OneEnum implements SomeInterface {
+        A1, A2, A3;
+    }
+
+    enum SecondEnum implements SomeInterface {
+        A1, A2, A3;
+    }
 }