Introduce dict[str, Performance]

[odashi]

Related to #491

This PR introduces following changes:

• Remove metric_name member from Performance.
• Change all list[Performance] to dict[str, Performance], whose keys are metric names.
• Refactoring related to these changes.

Originally, metric_name is used as a primary key of the list, and often the list is converted to dict in the library. This change attempts to removes this burden.

[pfliu-nlp]

Do we need to require that the performances need to maintain insertion order?

[neubig]

It would be nice to maintain this property. But it seems that as of Python 3.7, dicts are guaranteed to maintain insertion order: https://stackoverflow.com/questions/39980323/are-dictionaries-ordered-in-python-3-6

[odashi]

I don't think assuming any order is semantically good idea if we are using hashmap (dict) even if the language supports it. If the order of names is meaningful for someone, arranging the order should be the responsibility of callers.

[pfliu-nlp]

One high-level comment that could be considered as future PRs.

• refactoring metric_configs, overall and analyses to dict[str, ...] as well

[odashi]

One high-level comment that could be considered as future PRs.
refactoring metric_configs, overall and analyses to dict[str, ...] as well

Yes, I am planning to do it. The reason why this PR is proposed first is Performance is the most outer data structure that relies on metric names, and changing any inner structures affects this struct. I will propose other pull requests as well in the outer-inner manner.