graw/gdi: do not depend on UNICODE macro

graw/gdi: do not depend on UNICODE macro

Similar to the previous patch, we currently depend on the UNICODE macro
not being set, but it sometimes ends up getting set after all.

Unlike the previous patch, the easier thing to do here, is to lean into
the Unicode wrappers, and use the TEXT()-macro to define a Unicode
or ASCII literal, depending on the setting of the UNICODE macro.

Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5497>