feat: enable scaling mouse-scroll-multiplier for both precision and discrete scrolling

[twfksh]

Resolves Issue: #8670

Now precision and discrete scrolling can be scaled independently. Supports following configuration,

# Apply everywhere
mouse-scroll-multiplier = 3

# Apply separately
mouse-scroll-multiplier = precision:0.1,discrete:3 (default)

# Also it's order agnostic
mouse-scroll-multiplier = discrete:3,precision:2

# Apply one, default other
mouse-scroll-multiplier = precision:2

The default precision value is set 0.1, as it felt natural to me at least on my track-pad. I've also set the min clamp value precision to 0.1 as 0.01 felt kind of useless to me but I'm unsure.