Allow usage of star-tree index with null handling enabled when no null values in segment columns

[yashmayya]

• The star-tree index currently doesn't support null values (see Support StarTree index with nullHandlingEnabled #9981) and we skip using any star-tree indexes if query time null handling is enabled (https://docs.pinot.apache.org/developers/advanced/null-value-support#advanced-null-handling-support) -

  pinot/pinot-core/src/main/java/org/apache/pinot/core/startree/StarTreeUtils.java

  Lines 357 to 359 in 19b79f4

  	if (starTrees == null || queryContext.isSkipStarTree() || queryContext.isNullHandlingEnabled()) {
  	return null;
  	}

• However, we should still be using an existing star-tree index for a segment if there aren't actually any null values in that segment for the metrics being aggregated and the dimensions being filtered on.
• This patch introduces this additional conditional logic so that the star-tree index can be used in these situations. It's still important to introduce null value support in the star-tree index though, so that it can be used even when there are null values in the metric / dimension columns (along with being able to support predicates like IS NULL / IS NOT NULL).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 3.70370% with 26 lines in your changes missing coverage. Please review.

Project coverage is 63.83%. Comparing base (59551e4) to head (273ca9c).
Report is 1170 commits behind head on master.

Files with missing lines	Patch %	Lines
.../org/apache/pinot/core/startree/StarTreeUtils.java	3.70%	25 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #14177      +/-   ##
============================================
+ Coverage     61.75%   63.83%   +2.07%     
- Complexity      207     1534    +1327     
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  Files          2436     2622     +186     
  Lines        133233   144401   +11168     
  Branches      20636    22103    +1467     
============================================
+ Hits          82274    92174    +9900     
- Misses        44911    45432     +521     
- Partials       6048     6795     +747     

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[Jackie-Jiang]

Nice!