Leif/dependency improvements

[0xLeif]

This change allows for a trailing closure syntax when creating dependencies. This change also moved the addObserver of the notification NSUbiquitousKeyValueStore.didChangeExternallyNotification from the init to when icloudStore is first initialized.

@available(iOS 15.0, watchOS 9.0, macOS 11.0, tvOS 15.0, *)
extension Application {
    /// The default `NSUbiquitousKeyValueStore` instance.
    public var icloudStore: Dependency<NSUbiquitousKeyValueStore> {
        dependency {
            NotificationCenter.default.addObserver(
                self,
                selector: #selector(didChangeExternally),
                name: NSUbiquitousKeyValueStore.didChangeExternallyNotification,
                object: NSUbiquitousKeyValueStore.default
            )

            return NSUbiquitousKeyValueStore.default
        }
    }
}

This resolves a potential log error when you don't have the correct entitlement file.

Unable to find entitlement for KVS store

BUG IN CLIENT OF KVS: Trying to initialize NSUbiquitousKeyValueStore without a store identifier. Please specify your store identifier in the 'com.apple.developer.ubiquity-kvstore-identifier' entitlement.