C++ refactoring: argsort - remove workaround, use merge

[ianna]

No description provided.

[codecov]

Codecov Report

Merging #1140 (4a52773) into main (0b0fb3f) will increase coverage by 0.75%.
The diff coverage is 66.21%.

Impacted Files	Coverage Δ
src/awkward/_v2/behaviors/string.py	100.00% <ø> (ø)
src/awkward/_v2/forms/bitmaskedform.py	67.94% <ø> (ø)
src/awkward/_v2/forms/bytemaskedform.py	69.01% <ø> (ø)
src/awkward/_v2/forms/indexedform.py	72.00% <ø> (+8.84%)	⬆️
src/awkward/_v2/forms/unmaskedform.py	69.49% <ø> (ø)
src/awkward/_v2/highlevel.py	41.37% <ø> (+6.26%)	⬆️
.../awkward/_v2/operations/convert/ak_from_buffers.py	80.00% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_from_cupy.py	80.00% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_from_iter.py	80.00% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_from_jax.py	80.00% <0.00%> (ø)
... and 124 more

[ianna]

@jpivarski - this PR is complete. Please, check when you have time. Thanks!

[jpivarski]

The first time I wanted to actually use this CodeCov report, and it's not working! https://app.codecov.io/gh/scikit-hep/awkward-1.0/compare/1140/overview

I just wanted to see that the two new lines (self.mergeable) are covered, which would indicate that using mergeable/merge is as correct as the work-around. Anyway, if I have your word for it that this part of the code is covered, then you can merge this PR.

[jpivarski]

It is tested. (I checked out your branch, ran all the tests—success—then added an exception on the line I wanted to see if it was covered—it raised that exception—so we're good.)