sessiontxn/staleread: more accurate stale ts (#44272)

[ti-chi-bot]

This is an automated cherry-pick of #44272

What problem does this PR solve?

Issue Number: close #44215

Problem Summary:

What is changed and how it works?

When calculate as-of expr, calculate now expression by cached PD ts, the stale read ts will be more accurate, and there will also be less stale read fallback.

Check List

Tests

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

I also test with 100ms staleness read:

• resolved-ts.advance-ts-interval: 100ms

nightly:

this PR:

• resolved-ts.advance-ts-interval: 50ms

nightly:

this PR:

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Use more accurate stale read ts.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• cfzjywxk
• zyguan

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[you06]

/merge

[ti-chi-bot]

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

Commit hash: 8fac5d3

[you06]

/retest

[hawkingrei]

/retest