…rpc#33336)

As per discussion in grpc#32967.

… with pick_first (#33347)

Back-port #33336 to 1.56.

…_first (#33336)"

This reverts commit 6b4a1e4.

Fixes a problem seen when importing #33336.

…rpc#33336)

As per discussion in grpc#32967.

…33349)

Fixes a problem seen when importing grpc#33336.

…rpc#33336)

As per discussion in grpc#32967.

…33349)

Fixes a problem seen when importing grpc#33336.

…rpc#33336)

As per discussion in grpc#32967.

…33349)

Fixes a problem seen when importing grpc#33336.

#33340)

Currently, the outlier_detection policy reports ejection by intercepting
a subchannel's raw connectivity state watch. In the dualstack backend
design, we will instead want to report ejection via the health watch.
This PR is a first step toward that goal.

Specific changes in this PR:
- Add `type()` method to `InternalSubchannelDataWatcherInterface`, to
make it possible for LB policies to intercept data watchers.
- Use that mechanism in the outlier_detection policy to report ejection
both via raw connectivity state watches and via health watches. The hack
to prevent outlier_detection from working with pick_first from #33336
has been changed to affect only the raw connectivity watch, not the
health watch.
- Change health check client to fall back to reporting the raw
connectivity state if client-side health checking is not enabled. This
will allow pick_first to unconditionally start a health watch when it is
running under a petiole policy, which will be a no-op if neither health
checking nor outlier detection are configured.

Once we are done changing all of the petiole policies to delegate to
pick_first, we will remove the code that allows outlier_detection to
work via the raw connectivity state, so it will work only via the health
watch.

…state (#33427)

More work on the dualstack backend design:
- Now that all petiole policies have been changed to delegate to
pick_first, outlier detection no longer needs to eject via the
subchannel's raw connectivity state; it can now eject only via the
health state. See #33340.
- This also removes the now-unnecessary hack to explicitly disable
outlier detection in pick_first. See #33336.

grpc#33340)

Currently, the outlier_detection policy reports ejection by intercepting
a subchannel's raw connectivity state watch. In the dualstack backend
design, we will instead want to report ejection via the health watch.
This PR is a first step toward that goal.

Specific changes in this PR:
- Add `type()` method to `InternalSubchannelDataWatcherInterface`, to
make it possible for LB policies to intercept data watchers.
- Use that mechanism in the outlier_detection policy to report ejection
both via raw connectivity state watches and via health watches. The hack
to prevent outlier_detection from working with pick_first from grpc#33336
has been changed to affect only the raw connectivity watch, not the
health watch.
- Change health check client to fall back to reporting the raw
connectivity state if client-side health checking is not enabled. This
will allow pick_first to unconditionally start a health watch when it is
running under a petiole policy, which will be a no-op if neither health
checking nor outlier detection are configured.

Once we are done changing all of the petiole policies to delegate to
pick_first, we will remove the code that allows outlier_detection to
work via the raw connectivity state, so it will work only via the health
watch.

…state (grpc#33427)

More work on the dualstack backend design:
- Now that all petiole policies have been changed to delegate to
pick_first, outlier detection no longer needs to eject via the
subchannel's raw connectivity state; it can now eject only via the
health state. See grpc#33340.
- This also removes the now-unnecessary hack to explicitly disable
outlier detection in pick_first. See grpc#33336.