FIX: Selection highlight lingering after clicking save button (ISX-1482).

[graham-huws]

Description

Fix for ISX-1482 - Don't leave the Save Asset button as highlighted (focused) after clicking.

Changes made

As above.

Notes

Relating to my comments in the code, tabbing through the UI should highlight each object in turn per accessibility guidelines (https://unity.slack.com/archives/C3414V4UV/p1689871437531979?thread_ts=1689865302.307989&cid=C3414V4UV), so it's actually a bug that not everything gets highlighted when tabbing through the UI. But it's also one that seems to be extremely widespread across the whole editor, so probably not a top priority for us...

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.

[Pauliusd01]

LGTM, checked that the highlight disappears correctly on mouse click and tab+enter, double checked the IMGUI version that it still functions the same.

[lyndon-unity]

Code change looks reasonable (as does the change log tidy up)