more efficient Dice metrics for large num_class

[wyli]

• mostly from @myron's implementation
• remove is_binary_tensor checks, they are too expensive.
• remove the deprecated compute_meandice (use compute_dice instead)

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[wyli]

/build

[wyli]

/build

[myron]

Thank you for adding it, looks very good.
One small comment here
https://github.com/Project-MONAI/MONAI/blob/dev/monai/metrics/meandice.py#L206-L208

if we reach the last "return" statement, it seems to be guaranteed to be 0, so we don't need to calculate it