Deprecate Exp in favor of libraries implementation

[swernli]

Exp should arguably not be in the Microsoft.Quantum.Intrinsic namespace since it is advanced functionality that is non-trivial to implement across arbitrary inputs on hardware intrinsics (it requires array iteration, recursion, arithmetic operations, etc...). We should deprecate it in favor of a matching operation in the libraries. See related libraries issue for API discussion: microsoft/QuantumLibraries#579