SetMapMode(.., MM_TEXT) is called a lot in common gdiplus use cases via
gdi_transform_acquire(). Querying the size and resolution can be
expensive, so skip it when its not needed.

When running the "ZusiDisplay" ET423 diagnostic display, which uses
gdiplus heavily, this change increases the "indicator blinking speed"
from 0.6 per second to 1 per second and probably hits the FPS limit now.
Also, CPU usage of the ZusiDisplay.exe process goes down from ~75% to
~42% of one core according to "top", and wineserver CPU usage goes down
from ~48% to ~3%.
Signed-off-by: Florian Will <florian.will@gmail.com>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>