[FLINK-18464][Runtime] fix the bug voidnamespace cast to timewindow

[GuXiangFly]

What is the purpose of the change

This PR is to fix the following two issues only RocksDB:
https://issues.apache.org/jira/browse/FLINK-18464
https://issues.apache.org/jira/browse/FLINK-23036

Brief change log

If the passed namespaceSerializer does not match the namespace, it should not serialize and should not write backendState
Sharing state between trigger and TimeWindow causes inconsistencies in the namespace and NamespaceSerializer

Verifying this change

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

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This change is already covered by existing tests, such as (please describe tests).

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers:yes
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit 6085b34 (Fri Jun 18 15:27:05 UTC 2021)

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