Custom TTA modifications for detectron2

Implement both HFlip and VFlip as TTA transforms, add support for RotatedBoxes

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DatasetMapperTTAFlip

 DatasetMapperTTAFlip (min_sizes:List[int], max_size:int, flip:bool)

Implement test-time augmentation for detection data. Modified to implement both horizontal and vertical flip It is a callable which takes a dataset dict from a detection dataset, and returns a list of dataset dicts where the images are augmented from the input image by the transformations defined in the config. This is used for test-time augmentation.

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TTAPredictor

 TTAPredictor (cfg)

DefaultPredictor that implements TTA