core/backendoutput: Increase auto brightness curve resolution

In my setup at the moment, I have a window to the side and somewhat behind me, so light from that window hits the ambient light sensor at a diagonal angle. If I happen to shift my body enough to block or unblock the light's path from the window to the light sensor (even if only slightly), the brightness ends up changing even though the ambient light around the screen didn't actually change much if at all, and I then have to adjust the brightness back to where it was. Beyond that specific case, I generally feel like I have to adjust the brightness more often than if I just disabled the automatic brightness entirely, aside from if I go into a very dark room or turn the lights off.

I was never able to articulate what exactly is wrong about the curve beyond "it just doesn't work well", until I saw a blog post (https://zamundaaa.github.io/wayland,display/2026/04/24/automatic-brightness.html) explaining the system. Only then did I realize that the issue is likely that I generally prefer to keep the screen brightness between 20% and 40%, and since the curve only has points at 20% brightness steps it means that I'm stuck with linear interpolation between the 20% and 40% points rather than an actual "curve".

So, I tried making this change so that 11 control points are present instead of just 6, which as I understand it results in 10% brightness steps instead of 20%. So far, that makes the automatic brightness work much better for me, I'm definitely not forced to touch the brightness setting anywhere near as often, and even if I do out of habit I usually find that I end up just changing the brightness by less than 5% from what the automatic brightness gives me now.

For what it's worth my system is a Framework Laptop 13 with its built in ambient light sensor.