SimpleSinglePointerSelector: consider connecting pointer upon OnSourceDetected

[PJBowron]

Overview

When dealing with one or more pointer-providing motion controllers, the user may activate their controller after the app has begun to execute.

Expected Behavior

The activated controller becomes the primary controller.

Actual Behavior

Primary control remains with a previous controller (head-gaze, in the case of first controller activation)

Suggested change

In an internal project, we locally modified SimpleSinglePointerSelector and called ConnectBestAvailablePointer upon OnSourceDetected (if said controller SupportsPointingRay).

We'd like to contribute this change, if that sounds good?

[StephenHodgson]

Sounds good.

[david-c-kline]

This was released in the 2017.4.0.0 release candidate