add DAGRequestVerifier to verify tipb::DAGRequest

[SeaRise]

What problem does this PR solve?

Issue Number: ref #4118

Problem Summary:

What is changed and how it works?

Check List

Tests
We need a way to keep the validation logic once the DAGQueryBlock is removed.

• 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

None

[ti-chi-bot]

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