New drag widget with 3 values, akin to DragFloat3 in ImGui

**Is your feature request related to a problem? Please describe.**
I want to list the translation of a transform in one single row and have it be editable, right now I have to add 3 separate `DragValue`s to a `horizontal` which results in non uniformly sized boxes to drag, see [this](https://imgur.com/a/ujOfxjD) screenshot for a visual aid

**Describe the solution you'd like**
A new widget called `DragValue3` which creates 3 equally sized `DragValue`s in one row. Something like [this](https://imgur.com/a/wwRvEi4)

**Describe alternatives you've considered**
Adding 3 `DragValue` s to a horizontal row. This does work, but the boxes to change the values [aren't always the same size](https://imgur.com/a/ujOfxjD)

Start by tracing the existing DragValue widget and the horizontal layout API, since the issue names both as the current approach. Done means a DragValue3 widget presents three equally sized editable DragValue controls in one row, matching the requested transform-translation layout.

Written by the indexing model from the issue text.