Reduce code duplication and simplify ControlFlowNode and HLTControlFlowMgr

• Do not template CompositeNode on the 'type' of logic it performs; instead, use an enum and switch in the one place this matters. This should reduce the amount of code generated, and improve the variant visitation.
• Wrap the 'raw' std::variant of node types (now simplified/reduced) into a class to reduce the boiler plate required to use it.
• Move some common functions from BasicNode/CompositeNode into VNode
• Disentangle traversing nodes, and actions to be taken on the nodes
• Better string handling of nodeType

includes !4334 (closed)