Change ConcatCollector implementation to use off-heap

[npawar]

See #6770 for motivation

Pending: This PR only changes ConcatCollector. Will update RollupCollector in a following PR.

[codecov-commenter]

Codecov Report

Merging #6847 (dea93e3) into master (ac5aee7) will increase coverage by 30.01%.
The diff coverage is 72.80%.

@@              Coverage Diff              @@
##             master    #6847       +/-   ##
=============================================
+ Coverage     43.52%   73.53%   +30.01%     
- Complexity        7       12        +5     
=============================================
  Files          1421     1420        -1     
  Lines         69142    69842      +700     
  Branches       9987    10082       +95     
=============================================
+ Hits          30093    51359    +21266     
+ Misses        36504    15084    -21420     
- Partials       2545     3399      +854     

Flag	Coverage Δ	Complexity Δ
integration	43.35% <70.40%> (-0.18%)	7.00 <0.00> (ø)
unittests	65.51% <44.00%> (?)	12.00 <0.00> (?)

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

Impacted Files	Coverage Δ	Complexity Δ
...g/apache/pinot/core/util/GenericRowSerDeUtils.java	66.10% <66.10%> (ø)	0.00 <0.00> (?)
.../segment/processing/collector/ConcatCollector.java	89.74% <88.57%> (+9.74%)	0.00 <0.00> (ø)
...segment/processing/collector/GenericRowSorter.java	69.44% <100.00%> (+6.58%)	0.00 <0.00> (ø)
.../segment/processing/collector/RollupCollector.java	96.96% <100.00%> (+96.96%)	0.00 <0.00> (ø)
...e/segment/processing/framework/SegmentReducer.java	97.50% <100.00%> (+7.75%)	0.00 <0.00> (ø)
...a/manager/realtime/RealtimeSegmentDataManager.java	28.57% <0.00%> (-28.58%)	0.00% <0.00%> (ø%)
...ot/segment/local/customobject/MinMaxRangePair.java	75.86% <0.00%> (-24.14%)	0.00% <0.00%> (ø%)
.../starter/helix/HelixInstanceDataManagerConfig.java	78.04% <0.00%> (-21.96%)	0.00% <0.00%> (ø%)
...che/pinot/core/common/datatable/BaseDataTable.java	81.06% <0.00%> (-18.18%)	0.00% <0.00%> (ø%)
...mon/metadata/segment/OfflineSegmentZKMetadata.java	74.57% <0.00%> (-13.56%)	0.00% <0.00%> (ø%)
... and 939 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ac5aee7...dea93e3. Read the comment docs.

[Jackie-Jiang]

Mostly good

[npawar]

Addressed all comments @Jackie-Jiang

[Jackie-Jiang]

LGTM