[Backport to 3.0.x] freetype: use UCS-4 encoding on OS/2, too
This fixes subtitle texts are not shown correctly on OS/2.
Freetype module expects UCS-4 string. However, OS/2 iconv() does not support UCS-4 encoding, so UCS-2 encoding is used on OS/2. Because of this mis-match, subtitle texts on OS/2 are mis-interpreted. As a result, subtitle texts are not shown correctly.
(cherry picked from commit 89b561ea)
Conflicts: modules/text_renderer/freetype/freetype.c modules/text_renderer/freetype/text_layout.c