Make SIZE function work with s-expressions.

[dlurton]

Implements #30

Issue #, if available:

Description of changes:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #379 (69d647e) into master (7f76f53) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #379      +/-   ##
============================================
+ Coverage     81.63%   81.65%   +0.01%     
- Complexity     1307     1308       +1     
============================================
  Files           167      167              
  Lines         10222    10222              
  Branches       1671     1671              
============================================
+ Hits           8345     8347       +2     
+ Misses         1343     1342       -1     
+ Partials        534      533       -1     

Flag	Coverage Δ	Complexity Δ
CLI	17.62% <ø> (ø)	0.00 <ø> (ø)
EXAMPLES	74.85% <ø> (ø)	0.00 <ø> (ø)
LANG	84.19% <ø> (+0.02%)	0.00 <ø> (ø)
PTS	100.00% <ø> (ø)	0.00 <ø> (ø)
TEST_SCRIPT	79.68% <ø> (ø)	0.00 <ø> (ø)

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Impacted Files	Coverage Δ	Complexity Δ
...org/partiql/lang/eval/builtins/SizeExprFunction.kt	100.00% <ø> (ø)	3.00 <0.00> (ø)
...ng/src/org/partiql/lang/eval/EvaluatingCompiler.kt	83.37% <0.00%> (+0.27%)	158.00% <0.00%> (+1.00%)

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