Add compatibility checks (#120)

Author: rivera-ernesto

Sources/Grid/Grid+Inits.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 extension Grid {
     public init<Data, Item>(_ data: Data, @ViewBuilder item: @escaping (Data.Element) -> Item) where Content == ForEach<Data, Data.Element.ID, Item>, Data : RandomAccessCollection, Item : View, Data.Element : Identifiable {
         self.items = data.map { GridItem(view: AnyView(item($0)), id: AnyHashable($0.id)) }
@@ -14,6 +15,7 @@ extension Grid {
     }
 }
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 extension Grid {
     public init<C0: View, C1: View>(@ViewBuilder content: () -> Content) where Content == TupleView<(C0, C1)> {
         self.items = [GridItem(view: AnyView(content().value.0), id: AnyHashable(0)),

Sources/Grid/Grid.swift

@@ -1,6 +1,7 @@
 import SwiftUI
 
 /// A view that arranges its children in a grid.
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public struct Grid<Content>: View where Content: View {
     @Environment(\.gridStyle) private var style
     @State var preferences: GridPreferences = GridPreferences(size: .zero, items: [])

Sources/Grid/GridItem.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 struct GridItem: Identifiable {
     let view: AnyView
     let id: AnyHashable

Sources/Grid/Styles/ModularGridStyle.swift

@@ -1,6 +1,7 @@
 import SwiftUI
 
 /// Modular `Grid` style.
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public struct ModularGridStyle: GridStyle {
     public var columns: Tracks
     public var rows: Tracks

Sources/Grid/Styles/StaggeredGridStyle.swift

@@ -1,6 +1,7 @@
 import SwiftUI
 
 /// Staggered `Grid` style.
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public struct StaggeredGridStyle: GridStyle {
     public var tracks: Tracks
     public var axis: Axis

Sources/Grid/Styles/Style/EnvironmentValues+GridStyle.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public extension EnvironmentValues {
     var gridStyle: GridStyle {
         get {

Sources/Grid/Styles/Style/GridPreferencesModifier.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 struct GridPreferencesModifier: View {
     let id: AnyHashable
     let bounds: CGRect

Sources/Grid/Styles/Style/GridStyle.swift

@@ -1,13 +1,15 @@
 import SwiftUI
 
 /// A specification for the appearance of a `Grid`.
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public protocol GridStyle {
     var axis: Axis { get }
     var autoWidth: Bool { get }
     var autoHeight: Bool { get }
     func transform(preferences: inout GridPreferences, in size: CGSize)
 }
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public extension GridStyle {
     var axes: Axis.Set {
         self.axis == .horizontal ? .horizontal : .vertical

Sources/Grid/Styles/Style/GridStyleKey.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 struct GridStyleKey: EnvironmentKey {
     static let defaultValue: GridStyle = ModularGridStyle(columns: .min(100), rows: .fixed(100))
 }

Sources/Grid/Styles/Style/View+GridStyle.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 
+@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
 public extension View {
     /// Sets the style for `Grid` within the environment of `self`.
     @inlinable func gridStyle<S>(_ style: S) -> some View where S : GridStyle {