Add overloads that return tuples as default projections

[atifaziz]

This PR addresses #587.

[codecov]

Codecov Report

Merging #598 (7908cda) into master (66f7cab) will decrease coverage by 0.49%.
The diff coverage is 67.16%.

❗ Current head 7908cda differs from pull request most recent head 259c31f. Consider uploading reports for the commit 259c31f to get more accurate results

@@            Coverage Diff             @@
##           master     #598      +/-   ##
==========================================
- Coverage   92.63%   92.14%   -0.49%     
==========================================
  Files         113      113              
  Lines        3421     3488      +67     
  Branches     1056     1079      +23     
==========================================
+ Hits         3169     3214      +45     
- Misses        189      211      +22     
  Partials       63       63              

Files	Coverage Δ
MoreLinq/Pairwise.cs	94.11% <100.00%> (+0.36%)	⬆️
MoreLinq/CountDown.cs	88.23% <66.66%> (-2.09%)	⬇️
MoreLinq/TagFirstLast.cs	90.90% <66.66%> (-3.83%)	⬇️
MoreLinq/Lag.cs	92.10% <66.66%> (-4.77%)	⬇️
MoreLinq/Lead.cs	90.62% <66.66%> (-5.53%)	⬇️
MoreLinq/EquiZip.cs	91.37% <66.66%> (-4.54%)	⬇️
MoreLinq/ZipLongest.cs	76.66% <66.66%> (-4.29%)	⬇️
MoreLinq/ZipShortest.cs	78.78% <66.66%> (-4.55%)	⬇️
MoreLinq/Cartesian.g.cs	62.63% <66.66%> (+0.52%)	⬆️

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