Do background compaction when the ratio of stable data covered by delete range is too large

[lidezhu]

What problem does this PR solve?

Issue Number: close #3659

Problem Summary: If some segments was generated by logical split, the new segments will keep the delete range of the old segment. And by the old gc logic, the rows in stable covered by delete range is larger than the valid rows in the stable which will skip gc on these segments.
The original purpose of this check is to prevent small segments to merge delta. But after some detail investigation, this check is really unnecessary.

What is changed and how it works?

Check List

Tests

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

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

Fix the problem that obsolete data cannot be reclaimed after set tiflash replica to 0

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JaySon-Huang
• flowbehappy

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[lidezhu]

This is a cherry pick of #2416 and #3657

[lidezhu]

/run-all-tests

[lidezhu]

/run-all-tests

[lidezhu]

/run-all-tests

[lidezhu]

/run-all-tests

[CLAassistant]

All committers have signed the CLA.

[JaySon-Huang]

lgtm

[JaySon-Huang]

/rebuild

[lidezhu]

/merge

[ti-chi-bot]

@lidezhu: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 89d735c

[lidezhu]

/run-integration-tests