session, statistics: fix "data too long for column 'xxx_bound'" when analyze tables with very long strings

[time-and-fate]

What problem does this PR solve?

Issue Number: close #28793

Several columns in stats-related system tables are not long enough to hold long strings.

What is changed and how it works?

Change these columns from blob to longblob.

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

Fix "Data too long for column 'xxx_bound'" error when analyzing a table with strings longer than 65535 bytes.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• winoros
• wjhuang2016

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[time-and-fate]

/label needs-cherry-pick-5.1
/label needs-cherry-pick-5.2

[time-and-fate]

/run-check_dev

[qw4990]

/merge

[ti-chi-bot]

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

Commit hash: 280a452

[ti-srebot]

cherry pick to release-5.1 in PR #29072

[ti-srebot]

cherry pick to release-5.2 in PR #29073