[BugFix] Restore SHOW CREATE MATERIALIZED VIEW for sync MVs (backport #73396)

[mergify]

Sync MVs are mv indexes inside an OLAP table and are not registered as separate Tables in Database.idToTable / nameToTable. Since #43162 ("temporary table part-1") replaced the lookup in
showCreateInternalCatalogTable with MetaUtils.getSessionAwareTable, which throws SemanticException on miss, the existing fallback that scanned OLAP tables for a matching mv index has been unreachable - SHOW CREATE MATERIALIZED VIEW <sync_mv> has been failing with "Table ... is not found".

Catch SemanticException from the lookup and route MV-typed queries to a new findSyncMaterializedViewCreateStmt helper that performs the scan under DB READ (the indexNameToMetaId / indexMetaIdToMeta maps are HashMap-backed and mutated by ALTER, so the scan needs DB-wide exclusion). Non-MV queries rethrow the original "table not found" error unchanged.

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

---

This is an automatic backport of pull request #73396 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 4e35d9d has failed:

On branch mergify/bp/branch-4.0/pr-73396
Your branch is up to date with 'origin/branch-4.0'.

You are currently cherry-picking commit 4e35d9dc26.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   fe/fe-core/src/test/java/com/starrocks/catalog/MaterializedViewTest.java
	new file:   test/sql/test_materialized_view/R/test_show_create_sync_materialized_view
	new file:   test/sql/test_materialized_view/T/test_show_create_sync_materialized_view

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   fe/fe-core/src/main/java/com/starrocks/qe/ShowExecutor.java

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr

[kevincai]

@copilot help to resolve the backport code conflict in single commit.

[Copilot]

@copilot help to resolve the backport code conflict in single commit.

Resolved the backport conflict in ShowExecutor and fixed the related test compile issue on branch-4.0; targeted FE validation is passing on 2a720f0.

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