* Expression classes (nodes, aggregates, graphs, etc...) are now called BgNode, BgAggregate, etc...
* Evaluated and instantiated objects used by BuildGraph internals are now called BgNodeDef, BgAggregateDef, etc...
#preflight 62b6374161016695a6545b08
[CL 20818158 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]