Node values should not be children

Right now, a node's values are seen as generic ReaperNodes of that node. It would make more sense to flatten these out into to a dictionary.

Start by locating the parser's node and value model and the entry point that turns values into child ReaperNodes. Determine how the flattened dictionary should be represented and used by callers. Done means node values are exposed as dictionary entries rather than generic child nodes, with existing parsing behavior preserved.

Written by the indexing model from the issue text.