@acset_colim variant that preserves symbol -> part mapping #984

@acset_colim internally builds a mapping of symbols to parts, but this information is discarded when the final ACSet is returned. We should have a variant which allows one to retain access to this to prevent the need from manually inspecting the result to understand what this mapping is.

If we can create an enum type within the macro, then

Dom = @acset_colim' yGraph MyDomain begin
  v::V; e::E; src(e)==v
end

MyDomain.e == 1
MyDomain.v == 2

Clunkier alternative:

DomNames, Dom = @acset_colim' yGraph begin
  v::V; e::E; src(e)==v
end

DomNames[:e] == 1
DomNames[:v] == 2