[PERF] Greatly speed up Variable Length Concat

[samster25]

• before Were we using Arrow Growable for Concating UTF8 and Binary Arrays, which only allocated memory for the offset array
• Now we preallocate the value array since we know the complete size of the target array.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e4e8528) 85.19% compared to head (d608fdb) 85.19%.
Report is 2 commits behind head on main.

Additional details and impacted files

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  Coverage   85.19%   85.19%           
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  Files          55       55           
  Lines        5518     5518           
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  Hits         4701     4701           
  Misses        817      817