[DNM] rename ResolvedTS to Watermark

[zhangjinpeng87]

What problem does this PR solve?

Issue Number: close tikv/tikv#16708

What is changed and how it works?

Rename ResolvedTS to a more understandable name Watermark.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

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[ti-chi-bot]

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[ti-chi-bot]

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[ti-chi-bot]

@zhangjinpeng87: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-engine-integration-test	33b55dd	link	true	/test engine-integration-test
jenkins-ticdc/verify	33b55dd	link	true	/test verify
pull-cdc-integration-pulsar-test	33b55dd	link	true	/test cdc-integration-pulsar-test
pull-cdc-integration-mysql-test	33b55dd	link	true	/test cdc-integration-mysql-test
pull-cdc-integration-storage-test	33b55dd	link	true	/test cdc-integration-storage-test
pull-dm-integration-test	33b55dd	link	true	/test dm-integration-test
pull-cdc-integration-kafka-test	33b55dd	link	true	/test cdc-integration-kafka-test
pull-dm-compatibility-test	33b55dd	link	true	/test dm-compatibility-test

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[ti-chi-bot]

PR needs rebase.

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