[hotfix] Fix "doesn't exists" grammar typos

[Tsien4763]

What is the purpose of the change

This pull request fixes the grammatical typo doesn't exists to doesn't exist across the remaining applicable occurrences in Flink documentation, JavaDoc/comments, and user-facing error messages.

Brief change log

• Fix the typo in the DROP FUNCTION documentation.
• Fix the same typo in JavaDoc/comments and test comments.
• Fix the same typo in user-facing error messages where applicable.

Verifying this change

This change is a trivial text-only rework without test coverage. It does not change program behavior. The existing Azure CI is used to verify the branch.

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: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, 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

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Was generative AI tooling used to co-author this PR?

• Yes — ChatGPT (GPT-5.6 Sol)

Generated-by: ChatGPT (GPT-5.6 Sol)

[flinkbot]

CI report:

• 4d5caba Azure: SUCCESS
• 2a16e7b Azure: PENDING

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[spuru9]

Can you update the description as per the guidelines.

[spuru9]

Also I see multiple more similar typos can you fold them in (where applicable) while at it?

[Tsien4763]

Updated the PR description per the template and folded in the remaining applicable doesn't exists occurrences. The PR now covers 7 occurrences across documentation, comments/JavaDoc, tests, and user-facing messages. Thanks for pointing these out.

[spuru9]

LGTM

[dylanhz]

Thank you @Tsien4763. LGTM.