This commit is the final step in ensuring all the pipes commit what they
should. It also asserts this actually happens, enabling us to easily
catch future problems.
Generalize `FunctionStringMap` into `detail::GenericStringMap`, which
supports any `Depth=1` rank. `FunctionStringMap` remains as an `using`
with `Rank = ranks::Function`.
Replace the stub implementation of invalidation with the proper
implementation. A ReadPathCache is added to each global so that it can
keep tracks of what target are associated to which read paths.
By using this class we can create ptml::Tags without
XML tags. It is useful in the revng-c part when we
want to generate Plain C. All PTML Tags, from now on,
should be created via this class only.
In addition, port `Yield` library to be using this.
Giacomo Vercesi