Fix localized_comparator for macOS

[akirashirosawa]

Summary

SUMMARY: None

Purpose of change

As I wrote here Localized sorting #39873 not working for macOS:

for Russian on macOS it doesn't work at all :(

As you can see, words starting with а are interrupted by words starting with other letters.

for German on macOS too, it (not?) works.

I don't know German, but Kajak sorts before Käfer, so it works only for Latin characters, not for German special ones.

Describe the solution

As I suggest here, for macOS use CFStringCompare instead std::locale compare.

Describe alternatives you've considered

Somehow make std::locale compare to work correctly on macOS.

Testing

Results for Russian:

All is right order.

Results for German:

Käfer correctly sorts before Kajak and it's all i know about German :) (from example here #39873)

Additional context

More discussion here #40041

[jbytheway]

I think this could leak memory in the case where the CFString doesn't reuse the existing buffer. Based on the docs I think you should be calling CFRelease on the two created strings. But I'm not an OS X programmer, so I'm not totally sure.

[akirashirosawa]

@jbytheway Thank you for your comment. I read the docks and fixed a memory leak here #40131.