Factors out RunContext management into separate classes:
* Defines a LifecycleObject abstraction to manage initialization /
deinitialization
* Defines RunContextStack to enable a stack of init/deinit layers
* Defines a RunManager to own ensuring proper semantics for performing a
"single execution at a time" call while enabling a polymorphic base.
Implements Reset
Closes#5799
Unblocks #5800 (needs RunContext refactor too)
