statistics: add bench for MergeGlobalStatsTopNByConcurrency (#45998)

[ti-chi-bot]

This is an automated cherry-pick of #45998

What problem does this PR solve?

Issue Number: ref #45281

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

$ go test -run=^$ -bench=BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists -benchmem github.com/pingcap/tidb/statistics
goos: darwin
goarch: arm64
pkg: github.com/pingcap/tidb/statistics
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100-8           1000000000               0.0000725 ns/op               0 B/op          0 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size1000-8          1000000000               0.0006929 ns/op               0 B/op          0 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size10000-8         1000000000               0.006604 ns/op        0 B/op          0 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100000-8        1000000000               0.06678 ns/op         0 B/op          0 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size1000000-8       1000000000               0.6840 ns/op          0 B/op          0 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size10000000-8             1        6831699500 ns/op        1680005248 B/op 45000005 allocs/op
BenchmarkMergeGlobalStatsTopNByConcurrencyWithHists/Size100000000-8            1        73070549875 ns/op       16800008416 B/op        450000006 allocs/op

• 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

[hawkingrei]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hi-rustin, time-and-fate

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-14 07:06:20.188212118 +0000 UTC m=+528344.737228105: ☑️ agreed by time-and-fate.
• 2023-08-14 07:56:15.496464015 +0000 UTC m=+531340.045480002: ☑️ agreed by hi-rustin.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@dfe6238). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

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