[5.7] Fix(tester): TestResponse assertExactJson does not work for empty JSON objects

[alberthuang24]

Solved the problems mentioned in #25960 and #25769.

After the old decodeResponseJson directly operates on the response content json_decode($content, true), it is impossible to tell the difference between empty object and empty array.

$data = [
    'a' => new class {}
];

var_dump(json_encode($data)); 
var_dump(json_decode(json_encode($data), true)); 
var_dump(json_decode(json_encode($data)));


result: 

string(8) "{"a":{}}"
array(1) {
  ["a"]=>
  array(0) {
  }
}
object(stdClass)#4313 (1) {
  ["a"]=>
  object(stdClass)#4315 (0) {
  }
}

Therefore, if we want to distinguish between empty object and empty array, we need to change the second parameter $assoc to false.
But that's not compatible with the logic that preceded it. The assoc array is resolved to stdclass.
So. for compatibility, I have json_decode($data, true) and json_decode($data, false); Only get json_decode($data, false); The empty object inside is thus compatible with the previous logic, and the bug is fixed.

[taylorotwell]

I still have no idea what your method is doing. Give it a descriptive name and docblock.

[alberthuang24]

I still have no idea what your method is doing. Give it a descriptive name and docblock.

Hey, I re-implementation and Added detailed docblock.

[alberthuang24]

@taylorotwell

[alberthuang24]

poke @taylorotwell