Deprecate split view modifiers (#29)

After some experimentation I came to the conclusion that split view
"transitions" are not meant to be modified directly. They're not even a
thing in itself, really.

Instead, it should be the stack navigation view *within* the split view
that can and should have their transition modified directly.

So I deprecated all the split view modifiers and flattened the 2 stack
modifiers into one: `.navigationTransition`. In addition to this, a
useful runtime warning will let you know when you're holding it wrong.

This drastically simplifies the API surface to a single entry point and
is, I believe, a step in the right direction to easing the entry barrier
for this library.

Author: davdroman

Demo/Demo/Pages.swift

@@ -35,13 +35,13 @@ struct PageOne: View {
 struct PageTwo: View {
     var body: some View {
         let content = Group {
-            Text("The library is fully compatible with **NavigationView** in iOS 13+, and the new **NavigationStack** and **NavigationSplitView** in iOS 16.")
+            Text("The library is fully compatible with **NavigationView** in iOS 13+, and the new **NavigationStack** in iOS 16.")
             Text("In fact, that entire transition you just saw can be implemented in **one line** of SwiftUI code:")
             Code("""
-                NavigationView {
+                NavigationStack {
                   ...
                 }
-                .navigationViewStackTransition(.slide)
+                .navigationTransition(.slide)
                 """
             )
         }
@@ -62,7 +62,7 @@ struct PageThree: View {
             Text("The API is designed to resemble that of built-in SwiftUI Transitions for maximum **familiarity** and **ease of use**.")
             Text("You can apply **custom animations** just like with standard SwiftUI transitions:")
             Code("""
-                .navigationViewStackTransition(
+                .navigationTransition(
                     .fade(.in).animation(
                         .easeInOut(duration: 0.3)
                     )
@@ -71,7 +71,7 @@ struct PageThree: View {
             )
             Text("... and you can even **combine** them too:")
             Code("""
-                .navigationViewStackTransition(
+                .navigationTransition(
                     .slide.combined(with: .fade(.in))
                 )
                 """

Demo/Demo/RootView.swift

@@ -17,7 +17,7 @@ struct RootView: View {
                 .navigationViewStyle(.stack)
             }
         }
-        .navigationViewStackTransition(
+        .navigationTransition(
             appState.transition().animation(appState.animation()),
             interactivity: appState.interactivity()
         )

README.md

@@ -7,17 +7,16 @@
 <p align="center">
     <img width="320" src="https://user-images.githubusercontent.com/2538074/199754334-7f2f801d-1d9e-4cc4-a7a0-bb22c9835007.gif">
 </p>
-
 **NavigationTransitions** is a library that integrates seamlessly with SwiftUI's **Navigation** views, allowing complete customization over **push and pop transitions**!
 
 The library is fully compatible with:
 
-- **`NavigationView`** (iOS 13+)
-- **`NavigationStack`** & **`NavigationSplitView`** (iOS 16)
+- **`NavigationView`** (iOS 13, 14, 15)
+- **`NavigationStack`** (iOS 16)
 
 ## Overview
 
-Instead of reinventing entire navigation components in order to customize its transitions, `NavigationTransitions` ships as a simple set of 2 modifiers that can be applied directly to SwiftUI's very own first-party navigation components.
+Instead of reinventing entire navigation components in order to customize its transitions, `NavigationTransitions` ships with a simple modifier that can be applied directly to SwiftUI's very own first-party navigation component.
 
 ### The Basics
 
@@ -28,15 +27,7 @@ NavigationView {
   // ...
 }
 .navigationViewStyle(.stack)
-.navigationViewStackTransition(.slide)
-```
-
-```swift
-NavigationView {
-  // ...
-}
-.navigationViewStyle(.columns)
-.navigationViewColumnTransition(.slide, forColumns: .all)
+.navigationTransition(.slide)
 ```
 
 #### iOS 16
@@ -45,14 +36,7 @@ NavigationView {
 NavigationStack {
   // ...
 }
-.navigationStackTransition(.slide)
-```
-
-```swift
-NavigationSplitView {
-  // ...
-}
-.navigationSplitViewTransition(.slide, forColumns: .all)
+.navigationTransition(.slide)
 ```
 
 ---
@@ -62,23 +46,23 @@ The API is designed to resemble that of built-in SwiftUI Transitions for maximum
 You can apply **custom animations** just like with standard SwiftUI transitions:
 
 ```swift
-.navigationViewStackTransition(
+.navigationTransition(
     .fade(.in).animation(.easeInOut(duration: 0.3))
 )
 ```
 
 You can **combine** them:
 
 ```swift
-.navigationViewStackTransition(
+.navigationTransition(
     .slide.combined(with: .fade(.in))
 )
 ```
 
 And you can **dynamically** choose between transitions based on logic:
 
 ```swift
-.navigationViewStackTransition(
+.navigationTransition(
     reduceMotion ? .fade(.in).animation(.linear) : .slide(.vertical)
 )
 ```
@@ -129,13 +113,13 @@ The [**Demo**](Demo) app showcases some of these transitions in action.
 A sweet additional feature is the ability to override the behavior of the **pop gesture** on the navigation view:
 
 ```swift
-.navigationViewStackTransition(.slide, interactivity: .pan) // full-pan screen gestures!
+.navigationTransition(.slide, interactivity: .pan) // full-pan screen gestures!
 ```
 
 This even works to override its behavior while maintaining the **default system transition** in iOS:
 
 ```swift
-.navigationViewStackTransition(.default, interactivity: .pan) // ✨
+.navigationTransition(.default, interactivity: .pan) // ✨
 ```
 
 ## Documentation