Update EntityTypeInterface::getKeys() docs for string IDs

Created a quick MR.

Since this was directly in scope of the lines being touched, I opted to touch up two other things:
- Removed the note about the ID key being required. It is not, it is only required if you actually want to save the entity. That of course means in 99% of cases you do want to specify an ID key, but with contact messages in core we actually have an example of not having an ID, so it doesn't make much sense to claim it's required.
- Removed the usage of the term "Field API". It is a remnant of D7 times. In current times it is actually in correct because getKeys() is used for config entities as well and they have nothing to do with Field API in its current form. The more correct/current term would be "Entity API", but instead of replacing that I just removed the explicit mentioning of that as that would have felt somewhat out of place there.

I also noted that we use the term "property" there, to describe the values of the keys array. That's also somewhat incorrect, as for content entities, those are actually field names and properties are something different, but for config entities we do tend to use the term properties (for example ConfigEntityTypeInterface::getPropertiesToExport(), so I think it might be more clear to consistently use "field or property" instead of just "property". That would need to be changed a bunch of times, though, in that documentation paragraphs, so I anticipate that being flagged as too broad in scope for this issue.

@tstoeckler you used twice from at the @return array description .

 /**
   * Gets an array of entity keys.
   *
   * @return array
   *   An array describing how the certain information can be extracted <strong>from</strong>
   *   <strong>from</strong> entities of this entity type:

Nice catch, thanks! 👍

Seems pretty straightforward

@prem-suthar RTBC +1

@kleiton_rodrigues, There are contributor tasks → on Drupal.org that provide the steps for making useful additions to an issue. You may find How is credit granted for Drupal core issues → useful as well.

One comment on the MR.

Fixed

Also the MR is 250 commits back :) but you're right the comments would not cause those failures. Feedback from @catch appears to be addressed.

quietone → closed merge request !9177

Committed to 11.x and cherry-picked to 11.1.x

Thanks!