planner: move more methods from StatsHandle to its sub-packages

[qw4990]

What problem does this PR solve?

Issue Number: ref #46905

Problem Summary: planner: move more methods from StatsHandle to its sub-packages

What is changed and how it works?

planner: move more methods from StatsHandle to its sub-packages

No logical change, just refactor.

Check List

Tests

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

  • I checked and no code files have been changed.

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

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@qw4990: 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	9a95dc6	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	9a95dc6	link	true	/test check-dev2
idc-jenkins-ci-tidb/check_dev	9a95dc6	link	true	/test check-dev
idc-jenkins-ci-tidb/mysql-test	9a95dc6	link	true	/test mysql-test

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[qw4990]

See #47679