fix(color): Scale SF backlight value to user selected min/max backlight values

[philmoz]

Fixes #4057

Restrict the backlight value selected via the special function to lie between the user selected values for 'ON brightness' and 'OFF brightness' values.

When using a pot/slider to control the backlight the min value on the slider will be set to the 'OFF brightness' value, the max value will be 'ON brightness'. Values in between are scaled accordingly.

Tested on TX16S and EL18.

Note: If 'OFF brightness' is set to the lowest value in the settings UI then the inactivity timer will turn the LCD off. This is not true of the pot/sider value - the lowest value does not turn the LCD off.

[philmoz]

Updated the radio setup UI for backlight so that the ON slider can't go below the OFF value and the OFF slider can't go above the ON value.

[pfeerick]

Damnit... this collided with #4125 🤣

[philmoz]

Give me a little while to rebase things that might be affected by the recent merges.

[pfeerick]

Thanks, that seems to be working ok on TX16S, and is keeping the brightness SF within the bounds of the ON and OFF brightness sliders. Backlight can no longer jump to a higher brightness level when the inactivity timer kicks in.

[Neutral67fr]

Sorry I have to step in this discussion because I just jumped from 2.8.4 to 2.9.2 and can state that there actually is a flaw with backlight settings...
I have backlight set on S2 with GF. I can state that the radio seems to apply the "ON brightness" setting value 2 seconds after no user input (not "inactivity timeout" related), then will apply the "OFF brightness" setting value after the timeout.
Consequence is: When backlight GF setting is above ON brightness setting, the baclight increases after 2 s, and then the contrary (reduces if ON brightness setting is belows S2 setting).
So I get a neverending changing backlight level when using screen/buttons/sticks if both GF and ON brightness values are not equal...

Video here: https://drive.google.com/file/d/1dN6nbhgr7uitGb2rNAhHY7WyRpRaQqh8/view?usp=sharing

[philmoz]

The changes in this PR are not included in 2.9.x.
They will be in 2.10.