[BugFix] Resolve inconsistent global dictionary generation in flat JSON (backport #72953)

[mergify]

Why I'm doing:

The heterogeneous JSON detection logic did not correctly handle cases where:

a load batch did not generate a dictionary
a JSON path was extracted as a non-string type (such as int)

As a result, later dictionary collection could incorrectly ignore these values, causing dictionary loss and inconsistency across loads.

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 #72953 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 4c8f9c6 has failed:

On branch mergify/bp/branch-4.1/pr-72953
Your branch is up to date with 'origin/branch-4.1'.

You are currently cherry-picking commit 4c8f9c6128.
  (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:   be/src/storage/rowset/column_iterator.h
	modified:   be/src/storage/rowset/default_value_column_iterator.h
	modified:   test/sql/test_semi/R/test_flat_json_dict

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   be/src/storage/meta_reader.cpp

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