[PM-19659] Clean up Notifications code (#6244)

* Move PushType to Platform Folder

- Move the PushType next to the rest of push notification code
- Specifically exclude it from needing Platform code review
- Add tests establishing rules Platform has for usage of this enum, making it safe to have no owner

* Move NotificationHub code into Platform/Push directory

* Update NotificationHub namespace imports

* Add attribute for storing push type metadata

* Rename Push Engines to have PushEngine suffix

* Move Push Registration items to their own directory

* Push code move

* Add expected usage comment

* Add Push feature registration method

- Make method able to be called multipes times with no ill effects

* Add Push Registration service entrypoint and tests

* Use new service entrypoints

* Test changes

src/Core/Platform/PushRegistration/PushRegistrationData.cs

@@ -0,0 +1,31 @@
+namespace Bit.Core.Platform.PushRegistration;
+
+public record struct WebPushRegistrationData
+{
+    public string Endpoint { get; init; }
+    public string P256dh { get; init; }
+    public string Auth { get; init; }
+}
+
+public record class PushRegistrationData
+{
+    public string? Token { get; set; }
+    public WebPushRegistrationData? WebPush { get; set; }
+    public PushRegistrationData(string? token)
+    {
+        Token = token;
+    }
+
+    public PushRegistrationData(string Endpoint, string P256dh, string Auth) : this(new WebPushRegistrationData
+    {
+        Endpoint = Endpoint,
+        P256dh = P256dh,
+        Auth = Auth
+    })
+    { }
+
+    public PushRegistrationData(WebPushRegistrationData webPush)
+    {
+        WebPush = webPush;
+    }
+}