… (#12000)

See #11958

…esses and errors via ResolutionResult (#11997) (#12006)

Backport of #11997 to v1.72.x.
------
Fixes #11995

)

If the same exception is passed to multiple RPCs, then the results will race, which this fix addresses.

Fixes #11973

Co-authored-by: jiangyuan <joe469391363@gmail.com>

… onNext and onComplete (#11778) (#12021)

This prevents a NPE and subsequent channel panic when trying to build a
config (because there are no watchers, so waitingOnResource==false)
without any listener and route.
```
java.lang.NullPointerException: Cannot invoke "io.grpc.xds.XdsDependencyManager$RdsUpdateSupplier.getRdsUpdate()" because "routeSource" is null
    at io.grpc.xds.XdsDependencyManager.buildUpdate(XdsDependencyManager.java:295)
    at io.grpc.xds.XdsDependencyManager.maybePublishConfig(XdsDependencyManager.java:266)
    at io.grpc.xds.XdsDependencyManager$EdsWatcher.onChanged(XdsDependencyManager.java:899)
    at io.grpc.xds.XdsDependencyManager$EdsWatcher.onChanged(XdsDependencyManager.java:888)
    at io.grpc.xds.client.XdsClientImpl$ResourceSubscriber.notifyWatcher(XdsClientImpl.java:929)
    at io.grpc.xds.client.XdsClientImpl$ResourceSubscriber.lambda$onData$0(XdsClientImpl.java:837)
    at io.grpc.SynchronizationContext.drain(SynchronizationContext.java:96)
```

I think this fully-fixes the problem today, but not tomorrow.
subscribeToCluster() is racy as well, but not yet used.

This was noticed when idleTimeout was firing, with some other code
calling getState(true) to wake the channel back up. That may have made
this panic more visible than it would be otherwise, but that has not
been investigated.

b/412474567

) (#12088)