Provide a way to obtain the incoming stack height of a given ControlFlowNode

[zsr2531]

Summary:
Currently, Echo just throws away this information during the graph construction. It may be useful in some scenarios.

Suggestion:
A property would be ideal for this, the question is where to put the property. In ControlFlowNode or DataFlowNode?

[Washi1337]

The ControlFlowGraph model does not (and is not meant to) store information about stack heights or other types of data flow analysis. This is the job of a DataFlowGraph instead. A better place therefore to add this would be DataFlowNode. This way, the incoming stack height of a ControlFlowNode could be determined by getting the DataFlowNode associated to the block header instruction of the control flow node, and obtaining the absolute value from there.

[zsr2531]

Also, while we're at it... maybe adding additional information like the stack delta of a block is maybe information worth adding.