Hide (or option to hide) users with suspended enrolments in multiple areas

Will add link to Github repo.
Hope it's worth integration to core.
In this case, please review.

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NOTE: Suspended Users here mean users with suspended/inactive/expired/etc enrolments in a course.
Just could not find any other appropriate short term.

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This adds two helper functions in lib/accesslib.php and provides with the feature to remove Suspended Users (SU's) from the following parts of Moodle:

Course logs

• move SU's to a separate optgroup in the dropdown list of users
• option to exclude SU's from course logs;

Assignment 2.2

• submission list: add option to exclude SUs from the list
• remove suspended users from submitted assignments count (View X submitted assignments) based on above preference
• submission list: add SU symbol (as per current gradebook functionality)
• bulk assignment download: use above toggle
• individual assignment feedback: use above toggle when displaying Save and Next buttons

Assignment 2.3

• Same as above for Assignment 2.2

Gradebook

• Gradebook: Add 'Show only active enrolments' toggle in My Report Preferences
• Grader report: use above toggle
• User report: use above toggle to hide SUs, if set to 'No' then move SU's to a separate optgroup in the dropdown list of users
• Outcomes report: use above toggle
• Export: add 'Require active enrolment' checkbox

Quiz

• Attempts table: add checkbox 'Exclude suspended users' (default: checked)
• Quiz overview, link to Attampts table, 'Attempts: #': use above toggle
• 'Download table data as': use above toggle
• Quiz report graph: use above toggle
• User override: remove suspended users from user selection
• Quiz statistics: option to exclude SUs

Groups

• Auto create groups: do not include suspended users in Auto create groups
• Manually created: do not show SUs in potential members list
• Group overview page: move SUs to a separate optgroup in group member list

Workshop

• Submission table: remove suspended users from Workshop submission table
• Prevent from assessing submissions from SUs: remove SUs in get_all_submissions() function

Course search:

• Remove suspended teachers from course description