Warn on inlining explosion

[abadams]

We should be able to detect a combinatorial explosion due to recursive inlining by examining the Func graph, so that instead of the compiler just stalling, we can tell people that a certain chain of functions causes an expansion of work by a factor of x.

[kree-colemcalughlin]

This seems like an issue similar to the branching limit in specialize_branched loops. It would be nice to surface options to the user to control what the limit for these types of things are during a particular compilation. I think we discussed before introducing non-boolean valued options to Target.

In the case of inlining if the limit is reached does it make sense to fall back to another schedule at a certain level, like compute_root(), and warn the user? That way the code can at least compile.