Add a screen off button

Add a screen off button. In order not to wait for the backlight timer to expire. Just pressed the touch button on the screen and the screen went out, then touched the screen and it turned on, just like on the timer

Start by locating the touchscreen input handling and the backlight timer. Trace how a touch currently wakes the screen, then determine where a screen-off control would fit. Done means a touch action can turn the screen off before the timer expires and a subsequent touch turns it back on as described.

Written by the indexing model from the issue text.