EarlyStopper cannot deal with complex Metrics

[priba]

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🚀 Feature Request

EarlyStopper and ThresholdStopper cannot deal with complex Metrics such as MAP.

See:

https://github.com/mosaicml/composer/blob/8d4dfaf017369bc0d27bc4f707e0fa709005c7b5/composer/callbacks/early_stopper.py#L122

https://github.com/mosaicml/composer/blob/8d4dfaf017369bc0d27bc4f707e0fa709005c7b5/composer/callbacks/threshold_stopper.py#L100

This line should only convert the metric to a tensor if it is a numeric value. For complex metrics, we should either rely on self.comp_func and some distance metric or allow some way to extract the desired value in self.monitor. Otherwise it will also crash here when checking the absolute distance.

https://github.com/mosaicml/composer/blob/8d4dfaf017369bc0d27bc4f707e0fa709005c7b5/composer/callbacks/early_stopper.py#L128

Motivation

Metrics for object detection come as a dictionary. See MAP.