Enhancement: Introduces PagerInterface::isDeterministic (refs #8164)

[mvhirsch]

Subject

This is my suggestion to indicate an enduser that the list doesn't know how many elements ("all elements") will be affected by now. I decided to use a universal + sign to indicate it.

Default behavior:

Behavior SimplePager:

I'm not sure if I should add this to abstract Pager class without finalizing it. I rather suggest to implement abstract function isDeterministic and force any implementation of Pager to set it. WDYT? As this is not BC, I didn't choose this path (any custom implementation might be broken after a patch/minor update).

This refs #8164 but does not finally closes it. I'll update the way SimplePager count results using thresholds in a separate MR. Together they will solve #8164.

I am targeting this branch, because it's BC.

Refs #8164

Changelog

### Added
- Introduces `PagerInterface::isDeterministic` to render yet unknown result count in `SimplePager` properly

[VincentLanglet]

This is a good idea but it's a BC break to add a method in an interface.

You have to do like this

SonataAdminBundle/src/Filter/FilterInterface.php

Lines 22 to 25 in 672a614

	* @method array getFormOptions();
	* @method bool|null showFilter();
	* @method array getLabelTranslationParameters();
	* @method bool withAdvancedFilter();

By just adding a @method and it will be mandatory in next major.

[VincentLanglet]

Since the method is not mandatory, we might need an internal twig extension

public function isDeterministic(PagerInterface $pager): bool
{
     if (!method_exist($pager, 'isDeterministic')) {
         return true;
     }

     return $pager->isDeterministic();
}

[VincentLanglet]

There is maybe something to compute, because if we are on the last page and there is no next page, we know the exact number of result and we can return true.

[mvhirsch]

Sounds legit. I'll return this dynamically depending on currently known information!