FieldFilter should support absolute value

[haynesjm42]

FieldFilter should have a flag to use the absolute value of the value when being evaluated. Currently an app needs to make a CompoundFilter with the inverse operator and value in order to accomplish this.

Unsure it we need to worry about this in FilterChooser or other components, if not a ton of work then it probably makes sense but as a starting point the API should at least allow for it.

[amcclain]

Agreed this seems like an important add - thanks for filing.

Briefly wondered if it should be generalized into something like a valueTransform that could support additional tokens (e.g. case insensitive equals for strings), but that was the only other hypothetical usage I could think of at the moment. We privilege abs in our custom grid sorting, and given our domain it seems reasonable to give it a dedicated flag in field filter - don't want to over-complicate.

It's a good question how problematic it would be to release without FilterChooser / grid filters having a way to render / set this flag. Opens the possibility of a filter created programatically via another means displaying in FC, user could remove and then attempt to re-add it but would not be able to get it back to how it was. Guidance to devs could be to simply avoid this case - don't use the flag if you're also using FC - so I don't think it needs to be a blocker at all. But we would have a pretty strong desire to close that gap ... as soon as we had a chance to think through how that could actually work.