Add SEMANTIC_MATCH filter predicate for hidden semantic search layer

[xiangfu0]

Summary

• Registers SEMANTIC_MATCH(column, 'query text'[, topK]) as a Calcite SQL function in PinotOperatorTable
• Adds SEMANTIC_MATCH to FilterKind enum so it flows through the standard predicate pipeline
• Adds argument validation in CalciteSqlParser.validateFilter(): requires 2–3 args, column identifier as first arg, non-null string literal as second
• Adds a pass-through case in PredicateComparisonRewriter so the predicate is preserved for downstream rewriters

The intent is to support a hidden semantic search layer: a SemanticSearchQueryRewriter (in the StarTree extension) intercepts SEMANTIC_MATCH at query time, computes the embedding vector for the query text, then rewrites the predicate to VECTOR_SIMILARITY before execution. This PR provides the OSS hook that makes that rewrite chain possible.

Test plan

• Existing unit tests pass: CalciteSqlParser, PredicateComparisonRewriter, FilterKind usages
• Manual: verify SELECT ... FROM t WHERE SEMANTIC_MATCH(embedding_col, 'some query', 10) parses without error and round-trips through the rewriter chain unchanged
• Verify that an invalid call (wrong arg count, non-column first arg) throws IllegalStateException at parse time

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 18.75000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.97%. Comparing base (397704e) to head (f818df2).
⚠️ Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
...org/apache/pinot/sql/parsers/CalciteSqlParser.java	0.00%	9 Missing and 1 partial ⚠️
.../parsers/rewriter/PredicateComparisonRewriter.java	0.00%	2 Missing ⚠️
...ache/pinot/calcite/sql/fun/PinotOperatorTable.java	50.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (397704e) and HEAD (f818df2). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (397704e)	HEAD (f818df2)
java-21	5	4
unittests1	2	0
unittests	4	2
temurin	10	8
java-11	5	4

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #18191       +/-   ##
=============================================
- Coverage     63.13%   34.97%   -28.16%     
+ Complexity     1616      789      -827     
=============================================
  Files          3213     3229       +16     
  Lines        195730   196720      +990     
  Branches      30240    30414      +174     
=============================================
- Hits         123569    68800    -54769     
- Misses        62288   121855    +59567     
+ Partials       9873     6065     -3808     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-11	34.95% <18.75%> (-28.16%)	⬇️
java-21	34.96% <18.75%> (-28.13%)	⬇️
temurin	34.97% <18.75%> (-28.16%)	⬇️
unittests	34.97% <18.75%> (-28.16%)	⬇️
unittests1	?
unittests2	34.97% <18.75%> (+0.18%)	⬆️

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