CRM_Utils_Array::asColumns() - Add helper to rotate a matrix (from rows to columns)

[totten]

Overview

Add a helper function, asColumns(), which rotates an array-matrix -- converting from a row-orientation to a column-orientation.

Before

Helper does not exist.

After

Helper exists.

Technical Details

Suppose you have this data:

$alphabetByLetter = [
          // English column     // Greek column
  'a' => ['english' => 'eh',    'greek' => 'alpha'],
  'b' => ['english' => 'bee',   'greek' => 'beta' ],
];
// Assert: $rows['b']['greek'] == 'beta'

Then you rotate it, getting the data in columnar form:

$alphabetByLang = CRM_Utils_Array::asColumns($alphabetByLetter);

The resulting data is shaped like:

$alphabetByLang = [
                // "A" column      // "B" column
  'english' => ['a' =>'eh',        'b' => 'bee' ],
  'greek'   => ['a' =>'alpha',     'b' => 'beta'],
];
// Assert: $rows['greek']['b'] == 'beta'

[civibot]

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[eileenmcnaughton]

Stream of consciousness thoughts on merging this from chat

==tldr = merge-ready - give @colemanw a chance to input / say 'but x function already does that'

[colemanw]

Useful function with a test - good to merge IMO.

@eileenmcnaughton raised the question about what internal functions of CiviCRM we are obligated to maintain as a shared library for use by extensions. I agree we could be much more clear about that, but it doesn't have to block this PR.