Expand testing for expanded-view notifications

[hmalik88]

1. Updated the @metamask/notification-example-snap to have a method to trigger an expanded view notification.
2. Updated test-snaps to trigger the new methods added above.
3. Updated snaps-jest to allow for unit testing of expanded view notifications.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.74%. Comparing base (f21e859) to head (ca6b3dc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2956      +/-   ##
==========================================
+ Coverage   94.72%   94.74%   +0.02%     
==========================================
  Files         497      497              
  Lines       10825    10868      +43     
  Branches     1654     1669      +15     
==========================================
+ Hits        10254    10297      +43     
  Misses        571      571              

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