Add Scala 2.12 equivalent Iterator apply method for ByteString

actor-tests/src/test/scala/org/apache/pekko/util/ByteStringSpec.scala

@@ -814,6 +814,13 @@ class ByteStringSpec extends AnyWordSpec with Matchers with Checkers {
         }
       }
 
+      "created from iterator" in {
+        check { (a: ByteString) =>
+          val asIterator = a.iterator
+          ByteString(asIterator) == a
+        }
+      }
+
       "compacting" in {
         check { (a: ByteString) =>
           val wasCompact = a.isCompact

actor/src/main/scala-2.12/org/apache/pekko/util/ByteString.scala

@@ -39,6 +39,11 @@ object ByteString {
    */
   def apply(bytes: Byte*): ByteString = CompactByteString(bytes: _*)
 
+  /**
+   * Creates a new ByteString by iterating over bytes.
+   */
+  def apply(bytes: Iterator[Byte]): ByteString = CompactByteString(bytes)
+
   /**
    * Creates a new ByteString by converting from integral numbers to bytes.
    */
@@ -945,6 +950,14 @@ object CompactByteString {
     }
   }
 
+  /**
+   * Creates a new CompactByteString by traversing bytes.
+   */
+  def apply(bytes: Iterator[Byte]): CompactByteString = {
+    if (bytes.isEmpty) empty
+    else ByteString.ByteString1C(bytes.toArray)
+  }
+
   /**
    * Creates a new CompactByteString by converting from integral numbers to bytes.
    */