Remove BC layer for Pager service

Adding tags for contribution day at amsterdam2019.

We should briefly clarify the proposed resolution.

Proposed patch to remove BC layer for pager:

• removes usage of globals and deprecated pager.inc functions
• removes deprecation messages and tests wherever possible, including in constructors which now requires pager services

To be determined:

• How to handle Drupal\taxonomy\Form\OverviewTerms::__construct() parameters order if we make the pager manager required

Updated version of the patch, also removes pager.inc

Minor styling fix:
- Drupal\Core\Cache\Context\PagersCacheContext doesn't need to use PagerManagerInterface
- fix error that was already in Core code, where Drupal\views\Plugin\views\pager\SqlBase uses PagerParameters directly instead of PagerParametersInterface
- Improved reference to class function in code comment

Thanks @kim.pepper! Your re-rerolled patch worked against the HEAD of the 9.x branch, however in the meantime theme_preprocess_pager() was updated in #3094536: PHP 7.1 Warning: A non-numeric value encountered in template_preprocess_pager(). Re-rerolled with the fix.

I removed the DeprecatedArray mentions as well in this one (as PHP CodeSniffer reminded me :-)

I think we should also remove the deprecated requestStack property here?

Indeed, looking at #2044435: Convert pager.inc to a service and the current 9.0.x HEAD, it should be removed as PagersCacheContext does not extend RequestStackCacheContextBase anymore.

I went through the changes again and found no issue, I think this is good to go!

+++ b/core/lib/Drupal/Core/Pager/PagerManager.php
@@ -103,30 +102,6 @@ protected function getMaxPagerElementId() {
-  /**
-   * Updates global variables with a pager data for backwards compatibility.
-   */
-  protected function updateGlobals() {

In future we should use private scope for BC layers because if we really enforced API rules this is an API break.

Committed 8486c38 and pushed to 9.0.x. Thanks!