Add an option for enabling new data.table(<1-column matrix>) auto-naming behavior

[MichaelChirico]

Follow-up to #7149 for #7145. Confirmed all of {dtts}, {latrend}, {vardpoor} pass R CMD check under this branch.

Closes #7159; Closes #3193

NB: this has a conflict with #7156.

[github-actions]

• HEAD=dt-mat-opt slower P<0.001 for isoweek improved in #7144
  

Generated via commit 33f5ec0

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	2 minutes and 41 seconds
Installing different package versions	40 seconds
Running and plotting the test cases	2 minutes and 34 seconds

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.77%. Comparing base (67670e9) to head (33f5ec0).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7158   +/-   ##
=======================================
  Coverage   98.77%   98.77%           
=======================================
  Files          81       81           
  Lines       15185    15185           
=======================================
  Hits        14999    14999           
  Misses        186      186           

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