Only discover public methods annotated with @ScalarFunction

[richardstartin]

Stop discovering private scalar functions to avoid unpredictable illegal reflective access.

This is a breaking change; if a user has a non-public method annotated with @ScalarFunction then it will no longer be evaluated. The migration path is for the user to make the appropriate methods public, since they own the code.

[codecov-commenter]

Codecov Report

Merging #8544 (4596643) into master (900f01f) will decrease coverage by 41.30%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##             master    #8544       +/-   ##
=============================================
- Coverage     70.65%   29.35%   -41.31%     
=============================================
  Files          1674     1669        -5     
  Lines         87743    87602      -141     
  Branches      13279    13282        +3     
=============================================
- Hits          61999    25713    -36286     
- Misses        21439    59508    +38069     
+ Partials       4305     2381     -1924     

Flag	Coverage Δ
integration1	27.22% <0.00%> (+0.23%)	⬆️
integration2	25.89% <0.00%> (-0.22%)	⬇️
unittests1	?
unittests2	?

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

Impacted Files	Coverage Δ
...org/apache/pinot/common/function/FunctionInfo.java	87.50% <ø> (-12.50%)	⬇️
.../apache/pinot/common/function/FunctionInvoker.java	67.44% <ø> (-12.11%)	⬇️
...apache/pinot/common/function/FunctionRegistry.java	88.88% <0.00%> (-5.23%)	⬇️
.../java/org/apache/pinot/spi/utils/BooleanUtils.java	0.00% <0.00%> (-100.00%)	⬇️
...java/org/apache/pinot/spi/trace/BaseRecording.java	0.00% <0.00%> (-100.00%)	⬇️
...java/org/apache/pinot/spi/trace/NoOpRecording.java	0.00% <0.00%> (-100.00%)	⬇️
...ava/org/apache/pinot/spi/config/table/FSTType.java	0.00% <0.00%> (-100.00%)	⬇️
...ava/org/apache/pinot/spi/data/MetricFieldSpec.java	0.00% <0.00%> (-100.00%)	⬇️
...va/org/apache/pinot/spi/utils/BigDecimalUtils.java	0.00% <0.00%> (-100.00%)	⬇️
...java/org/apache/pinot/common/tier/TierFactory.java	0.00% <0.00%> (-100.00%)	⬇️
... and 1197 more

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[richardstartin]

It appears illegal reflective access is relied on even internally