API function/method: Get all WPSEO related capabilities

[JoryHogeveen]

Summary

This PR can be summarized in the following changelog entry:

• Add API function to get all WPSEO related capabilities.
  Props to: JoryHogeveen

Relevant technical choices:

Used the capability manager class instance.

Test instructions

This PR can be tested by following these steps:

Call the function. It should return the following:
Array ( [0] => wpseo_bulk_edit [1] => wpseo_edit_advanced_metadata [2] => wpseo_manage_options )

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes #9300

[JoryHogeveen]

For reference:

@moorscode mentioned https://github.com/Yoast/wordpress-seo/blob/trunk/wp-seo-main.php#L170-L174 as a difference in code order.
The last commit made this more in line with wp-seo-main logic.

This function shouldn't call add() from the capability factory because that method adds the capabilities to the roles which is not the purpose of this function.

[JoryHogeveen]

Note: Since 7.3 is out the version tag for this function should be updated before merging.

[afercia]

CR 👍

Of course, the @since notation should be updated before merge.

[Dieterrr]

Acceptance done 👍
Updated @since to 8.3.