Add ramp parameters.

[ttvd]

We would like to add support for Ramp type parameters in our Unreal plugin. Unfortunately there's no Slate widget which we can use for this purpose (or maps directly). This means we would have to create a custom Ramp widget.

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• [x] Add ramp parameter class and take care of construction (multiparm derivative).
• [x] Add UI construction.
  • [x] Float ramps.
  • [x] Color ramps.
• [x] Population of Slate widgets from Engine data.
  • [x] Float ramps.
  • [x] Color ramps.
• [x] Interacting with Slate widgets and triggering Engine cooks.
  • [x] Float ramps.
  • [x] Color ramps.
• [x] Serialization support.
  • [x] Float ramps.
  • [x] Color ramps.
• [ ] Undo / Redo support.
  • [ ] Float ramps.
  • [ ] Color ramps.

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Filed as RFE #73387 : Unreal: Add Ramp parameter type support.

[ttvd]

Referencing reported UE bug: https://answers.unrealengine.com/questions/380142/scolorgradienteditor-does-not-trigger-oncurvechang.html

[ttvd]

Filed as UE-27507 .