region_cache: filter peers on tombstone or dropped stores (#24726)

[youjiali1995]

What problem does this PR solve?

Problem Summary:
Backport some bug fixes.

What is changed and how it works?

What's Changed:
Cherry-pick #23695 and #24726.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test

Side effects

Release note

• Fix the issue that sometimes fails to send requests if there are tombstone stores.

[youjiali1995]

/run-all-tests

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• longfangsong
• sticnarf

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[JmPotato]

@youjiali1995 Any updates? Should we continue merging this PR into release-4.0?

[youjiali1995]

@JmPotato I have registered it in the v4.0.15 bug triage list. Waiting for triage.

[zhouqiang-cl]

/merge

[ti-chi-bot]

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

Commit hash: 68254b0

[ti-chi-bot]

@youjiali1995: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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