[BUG] Global memory is not persisted across cells in notebook

[Mogball]

Consider two separate cells:

var x: StringLiteral = "abcd"

print(x)

An empty string is printed, because string literals contain pointers to global memory, which are probably not getting persisted between cells as appropriate.

I'm not certain what the solution is: whether all global memory needs to be persisted or this is simply considered unsupported behaviour.

[walter-erquinigo]

Proper global memory handling should fix #638