Add support for contextual function nodes in the Binding Editor

[jdaignault]

Setting up a function-based nodes can feel a bit stiff. In the case of Call a Static Function it's especially tedious, given that the user has to explicitly:

• Create the Call a Static Function node
• Locate and set the owning class for the function they want to call
• Set the function they want to call
• Only at this point is it now safe to connect all the required inputs/outputs (ie. can't use a drag/drop operation from another node's output to automatically supply it as an input parameter, or vice-versa when originating from another node's input)

In contrast against the Event Graph, the user will generally:

• Drag from an existing value
• Type in a function name to filter selections down
• Select the relevant function

Function nodes are used very frequently for logical, math, and control flow operations, such that any workflow improvements made here would really improve the overall experience and save a lot of time in the long run.