A layer of Jetpack Compose-inspired code on top of Compose HTML

This module introduces the Jetpack Compose concept of `Modifier` but with an implementation designed to work well with
Compose HTML specifically (by delegating to its concept of `AttrBuilder`s and `StyleBuilder`s). It also
introduces a handful of foundation classes that use it, porting (a subset of) Jetpack Compose's foundation layer.

Note that, unlike the approach that Jetbrains is taking with their Multiplatform Widgets approach, this `Modifier`
class and its extension methods are _not_ trying to be 100% compatible with Android / Desktop compose. See the main
README's [What about Multiplatform Widgets](https://github.com/varabyte/kobweb#what-about-multiplatform-widgets) section
for more details on why.

> [!IMPORTANT]
> If you use this library directly without Silk, you must be sure to initialize its stylesheet, like so:
>
> ```kotlin
> fun main() {
>     renderComposable(rootElementId = "_kobweb-root") {
>         StyleSheet(KobwebComposeStyleSheet) // REQUIRED
>         ...
>     }
> }
> ```