MDL-46576 core_grades: MDL-47006 Refactor weightings code for readibility
MDL-46576 core_grades: MDL-47006 Change aggregationcoef2's comment
MDL-47006 core_grades: Fix float formatting

Part of MDL-46576
MDL-47006 core_grades: Add weightoverride to qualifies_for_regrading

Part of MDL-46576
MDL-47006 core_grades: Change category and item forms back to using

aggregationcoef and aggregationcoef2

Part of MDL-46576.
MDL-47006 core_grades: Fix handing of weight to aggregationcoef

Part of MDL-46576.