Child widgets do not maintain the Enhanced Input bindings from their parents

When a widget blueprint is created with Enhanced Input bindings in the event graph, when it is subclassed those bindings will not work in the child. This is inconsistent with how Actors function, and is also a regression from 5.4.

It appears to be a result of this commit (https://github.com/EpicGames/UnrealEngine/commit/5d2571bb36ab37410643e12d5a20909cc95d81c3) where bAutomaticallyRegisterInputOnConstruction is not set correctly in child widgets where there are enhanced input bindings on its parent.

A workaround is currently to have a dummy input action bound in the child, plugged into any node. This will cause all enhanced input bindings in the parent to now be bound correctly in the child.

Either see the attached repro project, or follow the steps from scratch here:

• Create a new 5.5 project
• Create a new map
• Create a widget blueprint, named widget A
• Create an input action and an input mapping context that maps the input action to any key
• In widget A, add the mapping context and create a binding for the input action
• In the level blueprint, create and add widget A to the viewport
• Play in PIE and observe that IA is triggered correctly when pressing the mapped key
• Create a new widget, widget B, that is a subclass of widget A
• Add this to the viewport instead
• Play in PIE and observe that the input action bound in the parent is no longer bound correctly in the child, as nothing is triggered
• If you perform a similar setup with Actors you will observe the child Actor has the parent's bindings as expected
• If you perform the same setup in 5.4 you will observe that the child widget has the parent's bindings as expected

Enhanced Input problems in 5.5