Merge branch '7.3' into 7.4

* 7.3:
  [Console] Fix `TreeHelper::addChild` when providing a string
  [Serializer] Handle invalid mapping type property type
  [Config] Do not generate unreachable configuration paths
  [WebProfilerBundle] Fix missing indent on non php files opended in the profiler
  [ObjectMapper] skip reading uninitialized values
  [JsonPath] Fix parsing invalid Unicode codepoints
  [FrameworkBundle] Fix cache warmers tests

Author: fabpot

Tests/Fixtures/hello_world.json

@@ -0,0 +1,4 @@
+[
+  "Hello",
+  "World!"
+]

Tests/Fixtures/hello_world.php

@@ -0,0 +1,4 @@
+<?php
+
+echo 'Hello';
+echo 'World!';