Replace the array_merge with spread array operator

[peter279k]

Q	A
Branch	v2.x
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Documented?	no
Fixed tickets	comma-separated list of tickets fixed by the PR, if any

• According to the reference, it's great to use the spread array operator to replace the array_merge function.
• There're two reasons about using the spread array operator:
  • Spread operator should have a better performance than array_merge and compile time optimization can be performant for constant arrays.
  • array_merge only supports array, while the spread operator also supports objects implementing Traversable.

New Task Checklist:

• [x] Are the dependencies added to the composer.json suggestions?
• [x] Is the doc/tasks.md file updated?
• [x] Are the task parameters documented?
• [x] Is the task registered in the tasks.yml file?
• [x] Does the task contains phpunit tests?
• [x] Is the configuration having logical allowed types?
• [x] Does the task run in the correct context?
• [x] Is the run() method readable?
• [x] Is the run() method using the configuration correctly?
• [x] Are all CI services returning green?

[veewee]

Thanks