Shouldn't `distlib.metadata.Metadata.dictionary` be renamed into `_dictionary` (or instead return the results equivalent to the ones returned by `todict`)?

[KOLANICH]

Is your feature request related to a problem? Please describe.
.dictionary and .todict() return different results for Metadata 2.1, which is confusing (one uses tab-completion, sees dictionary, reads it, sees the dict, but it turns out the dict is incomplete (i.e. 'project_url' and other keys form ._legacy are missing), and after digging into the source one understands that one needs to use .todict() instead).

Describe the solution you'd like

1. move .dictionary to ._dictionary.
2. optionally create a dictionary read-only property returning the same as .todict()