json: move _test.v files to vlib/json/tests/ (#22731)

vlib/json/json_encode_with_ptr_test.v

@@ -1,28 +0,0 @@
-import json
-
-struct User {
-	name string
-}
-
-struct MyStruct {
-	user   &User //
-	users  map[string]User
-	users2 map[string]&User
-}
-
-fn test_json_encode_with_ptr() {
-	user := User{
-		name: 'foo'
-	}
-	data := MyStruct{
-		user:   &user
-		users:  {
-			'keyfoo': user
-		}
-		users2: {
-			'keyfoo': &user
-		}
-	}
-
-	assert json.encode(data) == '{"user":{"name":"foo"},"users":{"keyfoo":{"name":"foo"}},"users2":{"keyfoo":{"name":"foo"}}}'
-}