Refactor CSS style classes to have a "Inherit", "Initial", etc. base class

[bitspittle]

This pattern is EVERYWHERE in our codebase:

class SomeCssStyle private constructor(private val value: String) : StylePropertyValue {
    override fun toString() = value

    companion object {
        // Keyword
        val Normal get() = SomeCssStyle("normal")
        val Whatever get() = SomeCssStyle("whatever")

        // Global
        val Inherit get() = SomeCssStyle("inherit")
        val Initial get() = SomeCssStyle("initial")
        val Revert get() = SomeCssStyle("revert")
        val Unset get() = SomeCssStyle("unset")
    }
}

We should probably run through and simplify it to something like:

abstract class <T: CssStyleProperty> CssStyleProperty protected constructor(private val value: String) {
        val Inherit get() = unsafeCast<T>("inherit")
        val Initial get() = unsafeCast<T>("initial")
        val Revert get() = unsafeCast<T>("revert")
        val Unset get() = unsafeCast<T>("unset")   
}

class SomeCssStyle private constructor(value: String) : CssStyleProperty<SomeCssStyle>(value) {
    companion object {
        // Keyword
        val Normal get() = SomeCssStyle("normal")
        val Whatever get() = SomeCssStyle("whatever")
    }
}