[libcxx] [test] Fix the monetary locale curr_symbol test on Windows, Apple and FreeBSD

International currency symbols (like USD, EUR) are returned with a
trailing space, like "USD ", on previously supported Unix platforms.
On Windows, the locales return them without a trailing space.

Also adjust the test for expecting a different unicode sequence for
the national currency symbol for ru_RU.UTF-8 and zh_CN.UTF-8.

Differential Revision: https://reviews.llvm.org/D120547