Generate a callsite identifier associated with each callsite

1. Generate a unique string name for a callsite that appears in every node
2. This identifier will refer to a single callsite and is used for trace data retrieval

@ke-yu
@lukechurch
@Steell
@Benglin

Good question...The callsite identifier is unique to every function call that appears in the script. It pertains to a single function call. As such, overloaded functions are taken care of because there will eb a callsite identifier for every call to a function whether it has an overload or not.

-  2 calls to the same function will have 2 callsites (and 2 therefore 2 unique identifiers)
- This mechanism doesn't know anything about the graph. If running in language only, there is only 1 guid