Move SparseArrays and Statistics to extensions

[jishnub]

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[codecov]

Codecov Report

Attention: Patch coverage is 5.88235% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 64.55%. Comparing base (023b1a4) to head (63d52bb).
Report is 9 commits behind head on master.

❗ Current head 63d52bb differs from pull request most recent head 736ad75. Consider uploading reports for the commit 736ad75 to get more accurate results

Files	Patch %	Lines
ext/ApproxFunBaseSparseArraysExt.jl	0.00%	16 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #506       +/-   ##
===========================================
- Coverage   75.20%   64.55%   -10.66%     
===========================================
  Files          79       83        +4     
  Lines        8445     8567      +122     
===========================================
- Hits         6351     5530      -821     
- Misses       2094     3037      +943     

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