executor: Use charset and collation from server vars for new schemas (#27216)

[ti-srebot]

cherry-pick #27216 to release-5.2
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---

What problem does this PR solve?

Issue Number: close #27214

Problem Summary:

CREATE SCHEMA should use the charset and collation from character_set_server and collation_server session/global vars if none are provided as part of the statement.

Check List

Tests

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

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

CREATE SCHEMA now uses `character_set_server` and `collation_server` for new schemas if none are provided as part of the statement

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• dveeden
• mjonss

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

[ti-srebot]

@dveeden you're already a collaborator in bot's repo.

[mjonss]

LGTM

[VelocityLight]

This pull request is closed because the related issue is triaged "Won't Fix".
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