bpo-28604: Fix localeconv() for different LC_MONETARY (GH-10606) (GH-10619)

bpo-28604: Fix localeconv() for different LC_MONETARY (GH-10606) (GH-10619)

locale.localeconv() now sets temporarily the LC_CTYPE locale to the
LC_MONETARY locale if the two locales are different and monetary
strings are non-ASCII. This temporary change affects other threads.

Changes:

* locale.localeconv() can now set LC_CTYPE to LC_MONETARY to decode
  monetary fields.
* Add LocaleInfo.grouping_buffer: copy localeconv() grouping string
  since it can be replaced anytime if a different thread calls
  localeconv().

(cherry picked from commit 02e6bf7f2025cddcbde6432f6b6396198ab313f4)