Replace hashmap with linked hashmap to fix schema order

[xinyual]

Description

This PR use linked hashmap to fix the schema order so the future IT won't be influenced by external variables like random seeds.

It influences several ITs. The fix is mainly divided into:

1. Add fields, for most IT, since we don't care about the schema order, like eventstats, we add a field so the current IT could pass
2. change expectation, especially for explain. Since the order is changed and logical plan is changed correspondingly, we change expectations.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]
#3739

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[opensearch-trigger-bot]

This PR is stalled because it has been open for 30 days with no activity.