Segresnet improvements (#5281)

This adds improvements to SegResNet semantic segmentation to include
deep supervision feature (among other things).

I've decided to add a new network named SegResnetDS instead of replacing
the existing SegResNet, because it would have broken all previously
pretrained model checkpoints.

Please take a look, and if it looks good, I can add unit tests. All the
helper functions, and blocks are inside of the same file (which I
prefer, since it's easier to read) instead of spreading it among other
files (e.g segresnet_ds_block or segresnet_utils).


### Description

A few sentences describing the changes proposed in this pull request.

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] 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.

Signed-off-by: myron <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Signed-off-by: KumoLiu <[email protected]>

Author: 2 people

monai/networks/nets/__init__.py

@@ -52,6 +52,7 @@
 from .regunet import GlobalNet, LocalNet, RegUNet
 from .resnet import ResNet, resnet10, resnet18, resnet34, resnet50, resnet101, resnet152, resnet200
 from .segresnet import SegResNet, SegResNetVAE
+from .segresnet_ds import SegResNetDS
 from .senet import (
     SENet,
     SEnet,