FIX: Canceling ControlScheme edits resets the UI to the previously saved values (ISX-1892)

[timkeo]

Description

The issue occurred because, although the changes weren't persisted to the SerializedProperty, the UI was still holding changes, and if the ControlScheme Edit dialog is re-opened (without changing ControlSchemes) the old values are displayed. We must explicitly reset the InputControlScheme in the ViewState to the last saved values.

Changes made

• Created ControlSchemeCommands.ResetSelectedControlScheme() command to reload InputControlScheme from the SerializedProperty (called during Cancel)
• Minor refactoring of "Close" methods in ControlSchemesView
• Added comments explaining current functionality

Notes

I don't know if the current functionality is what we want or not, and so I added verbose comments explaining how it works now. We can change it later if not to everyone's liking.

The new ResetSelectedControlScheme() command is nearly identical to SelectControlScheme. I decided this was the safer route for now, but maybe there's a better way.

I only did the most basic of testing before opening this PR.

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.

[ekcoh]

LGTM