[Refactor] Add PackSegInputs and some Transforms

mmseg/datasets/pipelines/__init__.py

mmseg/datasets/pipelines/formatting.py

mmseg/datasets/pipelines/loading.py

mmseg/datasets/pipelines/test_time_aug.py

mmseg/datasets/pipelines/transforms.py

tests/test_config.py

tests/test_data/test_formatting.py

tests/test_data/test_loading.py

tests/test_data/test_transform.py

tests/test_data/test_tta.py