Add advanced range-based platform version predicates

[davdroman]

This is a different take on #284 without overloading the introspect modifier, as suggested by @paescebu.

It reads quite clean, though it's a tiny bit more obscure to find (which might be a good thing, really), and it allows mixing current + current and past matching all in the same expression (which again, might be a good thing).

Examples:

import SwiftUI
@_spi(Advanced) import SwiftUIIntrospect

struct ContentView: View {
    @State var name = ""

    var body: some View {
        TextField("Name", text: $name)
            .introspect(.textField, on: .iOS(.v13...)) { textField in
                // do something with textField
            }
    }
}

struct ContentView: View {
    var body: some View {
        List {
            Text("Item 1")
            Text("Item 2")
        }
        .introspect(.list, on: .iOS(.v13, .v14, .v15)) { tableView in

        }
        .introspect(.list, on: .iOS(.v16...)) { collectionView in

        }
    }
}

[paescebu]

Yes!
I think that's perfect. It's an advanced use case which requires an "advanced" syntax.

That looks really beautiful 👌

But looks hard to maintain for you 😁

[davdroman]

Brilliant, glad we found the sweet spot. And maintenance is not a problem, that's what I'm here for 😄

I'll polish this branch over the weekend and probably merge by Monday.

[davdroman]

I guess the question is... should we still gate these? Maybe not 🤔

[davdroman]

I decided to keep it, and will also rename existing @_spi(Internals) annotations to @_spi(Advanced) in a separate PR, so everything is accessible from a single entry point. "Advanced" is also a better name than "Internals" because it denotes intent ("Advanced Mode").

[paescebu]

Sry for the late reply! I definitely think Advanced is such a better name. Internal really gives me "not intended for use" vibes.
With that convention I would say it encourages more advanced people to use it actually.
(Internal also made me a bit unsure initially and hence the question in #280)

[davdroman]

Some feature requests popped up yesterday so I'll merge this now and get a 0.8.0 release going later today.