[Enhancement] Reduce fragment plan size

[Seaven]

Fixes #issue

in complex query（a lot of union/expression/select-columns）, will make the fragment plan very large.
a SlotDescriptor size is 100 byte, 1000+ column will be 100k, so the whole fragment plan reach 1-2MB easily.
In x10 BE cluster, a FE's network output bandwidth will reach 10-20MB, and reach 500MB when FE support 50QPS

• Change unused paramter in thrift
• Add scalar operator rewrite when merge project

to handle union sql like:

select * from t0 union all select 1, 1, 1 from t1

before:

  4:Project
  |  <slot 10> : 16: cast
  |  <slot 11> : CAST(1 AS BIGINT)
  |  <slot 12> : CAST(1 AS BIGINT)
  |  common expressions:
  |  <slot 16> : CAST(1 AS BIGINT)
  |  
  3:OlapScanNode
     TABLE: t1
     PREAGGREGATION: ON
     partitions=0/1
     rollup: t1
     tabletRatio=0/0
     tabletList=
     cardinality=1
     avgRowSize=4.0

after:

  4:Project
  |  <slot 10> : 1
  |  <slot 11> : 1
  |  <slot 12> : 1
  |  
  3:OlapScanNode
     TABLE: t1
     PREAGGREGATION: ON
     partitions=0/1
     rollup: t1
     tabletRatio=0/0
     tabletList=
     cardinality=1
     avgRowSize=25.0

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

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.1
  • 3.0
  • 2.5
  • 2.4

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

0.0% Coverage
0.0% Duplication

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[wanpengfei-git]

[FE Incremental Coverage Report]

😍 pass : 25 / 25 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	com/starrocks/analysis/TupleDescriptor.java	4	4	100.00%	[]
🔵	com/starrocks/analysis/SlotDescriptor.java	16	16	100.00%	[]
🔵	com/starrocks/sql/optimizer/rule/transformation/MergeTwoProjectRule.java	5	5	100.00%	[]

[wanpengfei-git]

[BE Incremental Coverage Report]

😍 pass : 4 / 4 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	src/runtime/descriptors.cpp	4	4	100.00%	[]