CHANGE: UI module now defaults to having DefaultInputActions (case 1359306).

[Rene-Damm]

Fixes 1359306 (FogBugz).

Description

We landed a change previously (#1317) where behavior in the editor was no consistent with the player in that InputSystemUIInputModule would have no actions assigned to it by default. We previously added an AssignDefaultActions method that needs to be manually called to put the default actions in place.

This PR simply calls that method implicitly if the UI module has no input actions assigned to it.

Changes made

As part of putting the change in place, I discovered several other issues. See CHANGELOG.

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.