* Moved XML script parsing into UAT. We don't need to evaluate this in Horde.
* Added custom node types for script and expression nodes, rather than wrapping native nodes with a custom script task.
#preflight 62b31b76650c9d58579b2ea6
[CL 20773724 by Ben Marsh in ue5-main branch]
Nodes can now be implemented by arbitary C# methods. Graph structure is specified through expression trees implemented using Bg* types, which are not substituted with values until execution time. Doing so allows determination of node and option dependencies for a particular target, allowing us to generate dynamic UI for presenting relevant settings to the user.
Includes partial implementation of Installed Build script as an example implementation.
#preflight 61bb85d46c2686e86322eec9
[CL 18477305 by Ben Marsh in ue5-main branch]
