Add APL_USER_EVENT type request and require session if request type is it

[ysak-y]

What

Add Alexa.Presentation.APL.UserEvent type request and require session object if request type is it.

Why

Alexa.Presentation.APL.UserEvent type request is the kind of request that is called from SendEvent command of APL.

https://developer.amazon.com/en-US/docs/alexa/alexa-presentation-language/apl-interface.html#userevent-request
https://developer.amazon.com/en-US/docs/alexa/alexa-presentation-language/apl-standard-commands.html#sendevent-command

Sometimes I want to mock this type input but can't because VirtualAlexa doesn't know it. More specifically, Session object is needed to mock this request, but doesn't include because requiresSession object doesn't return true if Alexa.Presentation.APL.UserEvent.

So I want to add Alexa.Presentation.APL.UserEvent and add session object if this type of request coming.

How

Add Alexa.Presentation.APL.UserEvent type request to RequestType class by APL_USER_EVENT name. and return true if APL_USER_EVENT type request in requiresSession

[cfarmer-fearless]

Approving this because I would like to use it.