The use of function filectime() / filemtime() is discouraged

### Rule

I saw a warning similar to this in my IDE the other day:
```
The use of function filectime() / filemtime() is discouraged.
```
It was not coming from Magento CS but from PHPCS which I am currently using WITH Magento 2 CS.

If this check / warning is already there, would not be helpful to provide developers with some guidance or alternatives on what they can use instead?

### Reason

TBC: I am still doing some research to understand WHY the use of this is discouraged. I will complete this section with my findings.

### Implementation

[This guy](http://blog.tobiasforkel.de/en/2019/01/04/the-use-of-function-filectime-filemtime-is-discouraged-in-magento2/) proposes to use `\Magento\Framework\Filesystem\Driver\File`, same we are already advising to use to replace these kind of PHP functions.