FIX: Input devices sometimes marked as disabled on reconnect

[unity-cwells]

Description

If a InputDevice is disconnected while an app is out-of-focus and the the device's InputDevice.DeviceFlags.DisabledWhileInBackground flag is set, the flag will remain set upon reconnect even if the app has since regained focus. This results in the device incorrectly appearing as disabled until the next focus change event. This PR corrects this by clearing the InputDevice.DeviceFlags.DisabledWhileInBackground on reconnection of a device. If the app is still out-of-focus during reconnect and the flag is valid, this will be detected and set as normal during the call to InputManager.AddDevice().

Changes made

Fixed an issue where InputDevice.enabled could return false when a device was disconnected while an application was out-of-focus and then re-connected when in-focus

Checklist

Before review:

• Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • FogBugz ticket attached, example ([case %number%](https://issuetracker.unity3d.com/issues/...)).
  • FogBugz is marked as "Resolved" with next release version correctly set.
• Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

[Rene-Damm]

Needs test.