Add state and stateNullable helpers for KotlinBase

When Kotlin/Native exports to Objective-C, all custom classes share a common `KotlinBase` interface (which implements `NSObject` and has `isEqual` available).

We take advantage of this in order to add `state` and `stateNullable` helpers without requiring downstream users to define their own `equals` and `mappers`.

This simplification makes the library slightly easier to use and perhaps a little more intuitive. Instead of forcing callers through `state(_:equals:mapper:)` for custom types, it's possible to just use the simpler `state(_)` helper.

mvvm-flow/apple/xcode/mokoMvvmFlowSwiftUI/ViewModelState.swift

@@ -93,4 +93,12 @@ public extension ObservableObject where Self: ViewModel {
             mapper: { $0 as! Array<T> }
         )
     }
+
+    func state<T: KotlinBase>(_ flowKey: KeyPath<Self, CStateFlow<T>>) -> T {
+        return state(
+            flowKey,
+            equals: { $0.isEqual($1) },
+            mapper: { $0 }
+        )
+    }
 }

mvvm-flow/apple/xcode/mokoMvvmFlowSwiftUI/ViewModelStateNullable.swift

@@ -103,4 +103,12 @@ extension ObservableObject where Self: ViewModel {
             mapper: { $0?.localized() }
         )
     }
+
+    func stateNullable<T: KotlinBase>(_ flowKey: KeyPath<Self, CStateFlow<T>>) -> T? {
+        return stateNullable(
+            flowKey,
+            equals: { $0?.isEqual($1) == true },
+            mapper: { $0 }
+        )
+    }
 }