store/tikv: remove use of Priority transaction options in store/tikv

[disksing]

Signed-off-by: disksing i@disksing.com

What problem does this PR solve?

Usage of Priority option in store/tikv can be removed.

Part of #24302

What is changed and how it works?

What's Changed:

• move store/tikv/kv.Priority* back to kv.Priority*
• packages of TiDB use kv.Priority*
• define new tikv.Priority for client API
• add methods to update priority for KVTxn and KVSnapshot
• adapt types in driver

Check List

Tests

• Unit test

Release note

• No release note

[AndreMouche]

LGTM

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AndreMouche
• youjiali1995

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[disksing]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d1f08a0

[ti-chi-bot]

@disksing: Your PR was out of date, I have automatically updated it for you.

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/run-all-tests

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[disksing]

/run-check_dev_2