Revision 3b2b03f6c381a2408b32f670c07aed78f7be643b

EZP-29851: As a developer I want to be able to load several Locations at once, fast (#2493)

* EZP-29851: As a developer I want to be able to load several Locations at once, fast

Motivation
----------
Like the other bulk loading API's added recently this is to optimize usage in:
- Page builder
- Cronjobs / Commands
- GraphQL
- REST
- Admin UI
- Internally in Repository itself
- ...

These changes allows for less PHP code to execute, less SQL lookups, and less cache lookups by taking advantage of
Symfony Cache's multi get support.

Biggest benfit will be on setups where cache server is on a different machine, this can save ~5ms
for each and every lookup saved. Which can on complex landing pages mean saving up-to several seconds
of load time when HTTPCache is cold or disabled.

Design
------
Like other multi load API's return iterable list of objects, in this case Locations.
_Iterable as we might want to introduce custom collection in the future to expose more info, hence avoid hardcoding usage of plain PHP array type._

```
/**
* Return list of unique Locations, with location id as key.
*
* Missing items (NotFound) & those user does not have access to (Unauthorized), will be missing from the
* list and not cause any exception. It's up to calling logic to determine if this should cause exception or not.
*
* @param array $locationIds
* @param string[]|null $prioritizedLanguages Filter on and use as prioritized language code on translated properties of returned objects.
* @param bool|null $useAlwaysAvailable Respect always available flag on content when filtering on $prioritizedLanguages.
*
* @return \eZ\Publish\API\Repository\Values\Content\Location[]|iterable
*/
public function loadLocationList(array $locationIds, array $prioritizedLanguages = null, bool $useAlwaysAvailable = null): iterable;
```

* Fix review comment in regards to REST Client fix

* Fix review comment on SiteAccessAware repo tests return value usage