Merge conflicts resolved
fixed formatting issue
Moved chain input filter to base class
Update InputFilter.php
Update InputFilterTest.php
Revert "Update InputFilterTest.php"

This reverts commit d40f8d749e411781ddc615349259d7e38001fbb4.
Revert "Update InputFilter.php"

This reverts commit af6681dbe38feaf80f72e65af6d0f11b939a692a.
Removed extra new lines
Renamed chain method to merge, removed fluid interface on method
Renamed mergeInputFilter to merge so it matches the input method name
#6431 - return type-hint fix
#6431 - adding missing `@group` docblock and cleaning up test logic for readability
Merge branch 'feature/#6431-input-filter-merge-support' into develop

Close #6431