meta: add an in-memory autoID allocator

[djshow832]

What problem does this PR solve?

Problem Summary: add an in-memory autoID allocator for temporary tables.
Part of #24169

What is changed and how it works?

What's Changed: define an inMemoryAllocator.

How it Works: allocate autoID in memory.

Related changes

• N/A

Check List

Tests

• Unit test

Side effects

• N/A

Release note

• Add an in-memory autoID allocator.

[AilinKid]

/home/jenkins/agent/workspace/tidb_ghpr_check/go/src/github.com/pingcap/tidb/meta/autoid/autoid.go:1026:65: unnecessary conversion

[AilinKid]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• tangenta

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[djshow832]

/merge

[ti-chi-bot]

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

Commit hash: 57f5946

[ti-chi-bot]

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