ddl: abstract ingest backend related structures to interfaces

[tangenta]

What problem does this PR solve?

Problem Summary:

This is the code refactoring, let's skip the issue check.

What is changed and how it works?

After this PR, we can move the tests in realtikvtest/addindex to ddl package, and create index in ingest mode based on unistore. The cost can be reduced a lot.

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

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• wjhuang2016
• zimulala

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[zimulala]

LGTM

[Benjamin2037]

LGTM

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: cfb9a12

[ti-chi-bot]

@tangenta: 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
idc-jenkins-ci-tidb/unit-test	2406c1f	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	2406c1f	link	true	/test check-dev2

Full PR test history. Your PR dashboard.

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