[BugFix] Relax DB lock to intensive path in qe/ read-only paths (backport #73067)

[mergify]

Switch four single-table read paths in qe/ from full DB READ to IS+table-READ via lockTableWithIntensiveDbLock so they no longer block concurrent DDL on other tables in the same database.

• ShowExecutor.showCreateInternalCatalogTable: move lookup outside the lock; revalidate the resolved Table reference once the intensive lock is held so concurrent DROP/RENAME between lookup and lock acquisition is reported as ERR_BAD_TABLE_ERROR rather than serving DDL from a stale Table.
• ShowExecutor.visitShowTabletStatement (both branches): use the known/resolved tableId for table-READ; the table-by-name branch also revalidates after locking. The single-tablet branch already re-fetches under the lock and needs no extra check.
• ConnectProcessor.handleFieldList: move lookup outside the lock; collapse the nested lock-try inside the connector-exception try into a single try-catch-finally; revalidate after locking for internal-catalog DBs (external catalog tables are not tracked by LocalMetastore).

The revalidation closes a TOCTOU window: under the old DB READ, DROP/RENAME could not interleave between lookup and use; under IS+table-READ the lookup is unprotected so the resolved Table can be removed from the DB before the lock is taken. Re-fetching by id after locking and comparing references catches that window and reports the table as not-found, matching the old semantics.

Why I'm doing:

What I'm doing:

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5
  • 3.4

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This is an automatic backport of pull request #73067 done by [Mergify](https://mergify.com).