st3m_gfx: improve naming of set_mode and get_mode

components/micropython/usermodule/mp_sys_display.c

components/st3m/st3m_gfx.c

components/st3m/st3m_gfx.h

components/video_mpeg/video_mpeg.c

python_payload/apps/clouds/__init__.py

python_payload/apps/mandelbrot/4bit.py

python_payload/apps/mandelbrot/__init__.py

python_payload/st3m/application.py

python_payload/st3m/ui/elements/overlays.py

sim/fakes/sys_display.py