[BugFix][FlatJson] Fix flat json bugs

[Seaven]

Why I'm doing:

• Fix flat json time profile lose
• Fix flat json choose subfield strategy
  • first sort by sparsity factor, then column name
• Fix flat json function concurrent bug
  • json function context init flag set early

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 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
  • 3.3
  • 3.2
  • 3.1
  • 3.0
  • 2.5

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

❌ fail : 12 / 62 (19.35%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	be/src/connector/lake_connector.cpp	0	22	00.00%	[725, 726, 728, 734, 735, 737, 748, 749, 751, 759, 760, 761, 762, 764, 765, 766, 768, 769, 770, 772, 773, 774]
🔵	be/src/exec/pipeline/scan/olap_chunk_source.cpp	0	23	00.00%	[656, 660, 661, 663, 669, 670, 672, 683, 684, 686, 694, 695, 696, 697, 699, 700, 701, 703, 704, 705, 707, 708, 709]
🔵	be/src/util/json_flattener.cpp	6	9	66.67%	[514, 517, 518]
🔵	be/src/storage/rowset/json_column_iterator.cpp	4	6	66.67%	[137, 138]
🔵	be/src/exprs/json_functions.cpp	2	2	100.00%	[]

[github-actions]

@Mergifyio backport branch-3.3

[mergify]

backport branch-3.3

✅ Backports have been created

• #50292 [BugFix][FlatJson] Fix flat json bugs (backport #50223) has been created for branch branch-3.3