feat: add SliderSetting

[Suor]

Adds SliderSetting — looks like RangeSetting that operates over a fixed array of values instead of a range plus step. Works as a more convenient and glancable alternative for both RangeSetting and EnumSetting.

Examples from Bro Studio and Challanges mods:

1. Skip boring values:

::Challenges.SliderSetting("foodPriceMult", 1,
    [1, 2, 3, 5, 10, 20], null,
    "Food Price Multiplier");

2. Using non-numeric qualitative values:

page.add(::BroStudio.SliderSetting("attrsVeteranBoostValue", "off",
    ["off" "slight" "classic" "high"],
    null,
    "Veteran Boost", ...));

# or only qualitative labels with numbers under the hood

page.add(::BroStudio.SliderSetting("attrsVeteranBoostValue", 0,
    [0, 0.1, 0.1667, 0.25],
    ["off" "slight" "classic" "high"],
    "Veteran Boost", ...));

3. Mix those two:

def.add(::Challenges.SliderSetting("maxItemsPerBattle", -1,
    [-1, 5, 4, 3, 2, 1, 0],
    ["off" "5" "4" "3" "2" "1" "none"],
    "Max Equipment Drops Per Battle", ...));

[Suor]

The widget was heavily tested in this form within Bro Studio. The js code might be merged with RangedSetting one though to make it both less monkey and less self-contained.

[TaroEld]

Looks good conceptually, I'll rewrite the JS code to be less monkey as you mentioned.