Added ToString() override based on PointerInputModule

[BaalEvan]

Description

PreviewGUI is missing in new Input System so i added toString Method based on PointerInputModule

Changes made

Added ToString override to InputSystemUIInputModule

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.

[unity-cla-assistant]

All committers have signed the CLA.

[ekcoh]

If work is resumed on this PR it must be updated with latest changes from develop to not cause CI issues.

[BaalEvan]

There is no more work to be done; it's just a single method and a removed comment with ////TODO: ToString() method a la PointerInputModule waiting for review (or any feedback) for 4 years xD @ekcoh