Better HttpHeaders Copying (Azure#30860)

sdk/core/azure-core/src/main/java/com/azure/core/http/HttpHeaders.java

@@ -69,6 +69,14 @@ public HttpHeaders(Iterable<HttpHeader> headers) {
         }
     }
 
+    HttpHeaders(HttpHeaders headers) {
+        this.headers = new HashMap<>((int) (headers.headers.size() / 0.75f));
+        // TODO (alzimmer): This, and the API above, should be copying using the value list as this will String
+        //  join multiple values. Or, better yet provide better copy methods on HttpHeader and Header.
+        headers.headers.forEach((key, value) ->
+            this.headers.put(key, new HttpHeader(value.getName(), value.getValue())));
+    }
+
     /**
      * Create a HttpHeaders instance with an initial {@code size} empty headers
      *