Filter columns in list-view are not retained for Duplicate customfields, there is one occurrence for duplicate fields in dropdown

Issue Summary

This behavior might occur with multiple/duplicate custom fields.

Columns under list-view for Filter option are not retained with multiple/duplicate customfields.

The issue arises because there are some parts of the API and/or UI code that are case sensitive, and some that are not. i.e. some code is treating DUPLICATE FIELD[Dropdown] and Duplicate Field[Dropdown] as a collapsed custom field, while other parts of the code think they are totally separate.

Additionally, after drag-and-dropping columns to re-order them, it submits an API request with a specific `cfid` for the field instead of it's more human readable name. Which means columns may not be supporting collapsed fields properly in the first place.

Steps to Reproduce

1. Create multiple custom fields with the same name, some of them in lower case and a few in upper case. 
2. Create a filter
3. Switch to 'List view'
4. Select 'Column' >> 'Filter'
5. Select the customer field (let's say with Upper case)
6. Save
7. Change the location of the column by dragging it left or right.
8. Selected custom field will disappear from the filter result/ screen.

Screenshot from browser logs

Expected Results

Selected custom fields should be retained on the filter result/screen.

Actual Results

Observation 1: Selected custom field is not retained on the screen.

Observation 2: Another observation, Dropdown for fields under column >> Filter shows one field of each type (single select, multiple select, checkbox).

Workaround

A possible workaround at the moment is to differentiate these custom fields with different text (not different casing- upper/lower case will not help to differentiate customfields)