This internal type is used to collect things about a process like the
memory maps, address layout, and symbol cache. This can persist once
parsed at startup, then applied to objects created on demand such as the
SysprofDocumentProcess or used by symbolizers internally rather than
complicated function arguments.
This isn't what it will look like in final form, just get the minimum
there for us to use it with the bundled decoder (copied from libsysprof
with adaptations).
This exposes the types and hierarchy but won't expose the API details that
we need internally. The idea here is that we can keep that private so we
can adjust how it is used should we need to since the public interface
would be the SysprofDocumentSymbols, not the SysprofSymbolizer which does
decoding directly via address/context state.
