Added Pos and Neg operators.

[lziq]

Motivation:
As we are replacing ExprNode with PIG-generated AST, we need to resolve the inconsistency between them.

With 2 or more arguments provided, ExprNode uses NAry.add(NAry.Sub) to model the addition operator, while PIG-generated AST uses Plus(Minus) to model it. However, with only one argument provided, the addition operator is modeled as Pos(Neg) in PIG AST, while in ExprNode it is still NAry.add(NAry.Sub).

This PR aims to resolve this inconsistency.

Suggested reviewing order:

1. SqlParser.kt and EvaluatingCompiler.kt
2. ExprNodeToStatement.kt and StatementToExprNode.kt.
3. Other files.

[codecov-commenter]

Codecov Report

Merging #532 (7494ec0) into deprecate-exprnode (d165c77) will decrease coverage by 0.07%.
The diff coverage is 65.21%.

@@                   Coverage Diff                    @@
##             deprecate-exprnode     #532      +/-   ##
========================================================
- Coverage                 80.72%   80.64%   -0.08%     
- Complexity                 1694     1696       +2     
========================================================
  Files                       196      196              
  Lines                     14387    14413      +26     
  Branches                   2977     2985       +8     
========================================================
+ Hits                      11614    11624      +10     
- Misses                     1811     1819       +8     
- Partials                    962      970       +8     

Flag	Coverage Δ
CLI	26.53% <ø> (ø)
EXAMPLES	74.49% <ø> (ø)
LANG	82.43% <65.21%> (-0.09%)	⬇️
PTS	∅ <ø> (∅)
TEST_SCRIPT	76.92% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ng/src/org/partiql/lang/ast/ExprNodeToStatement.kt	92.66% <50.00%> (-1.11%)	⬇️
...al/visitors/StaticTypeInferenceVisitorTransform.kt	78.46% <50.00%> (-0.67%)	⬇️
lang/src/org/partiql/lang/syntax/SqlParser.kt	76.83% <50.00%> (-0.17%)	⬇️
...ng/src/org/partiql/lang/eval/EvaluatingCompiler.kt	79.27% <75.00%> (-0.11%)	⬇️
...ng/src/org/partiql/lang/ast/StatementToExprNode.kt	92.12% <100.00%> (+0.58%)	⬆️
...c/org/partiql/lang/ast/passes/StatementRedactor.kt	80.00% <100.00%> (-0.89%)	⬇️

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[am357]

Could we also have the motivation in the PR notes (or the related issue if there is one)?

[alancai98]

A couple typos in the EvaluatingCompiler and a couple nits in the inferencer. Could you also add more context for this PR? May want to mention that ExprNode had modeled unary + and - as the same as NAry, while PartiqlAst models them as separate nodes.

[alancai98]