Revision 1885953

Follow up to r1882234, r1882235,r1882313: Fix file name encoding issue
when invoking editor on Windows.

* subversion/libsvn_subr/cmdline.c
  (): include apr_env.h for apr_env_get
  (find_editor_binary):
    - Change the encoding to set to EDITOR, from active code page to
      UTF-8 on Windows.
      - Transcode editor_cmd to UTF-8.
      - Use apr_env_get() instead of getenv().
      - Transcode config setting for SVN_CONFIG_OPTION_EDITOR_CMD.
    - Add pool argument for transcoding and getting environment variables.
  (svn_cmdline_edit_file_externally, svn_cmdline_edit_string_externally):
    - Use _wsystem() instead of system() on Windows environment.
    - Enclose whole command strings with double quotes[1] in _wsystem().

[1] https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/cmd

Suggested by: jun66j5
              (editor return value in find_editor_binary)