fix: snackbar: added lastfocusableElement prop

[rmotwani-c-eightfold]

SUMMARY:

• Added a prop lastFocusableElement which takes the reference of the element which triggers the snackbar
• So that on close of the snackbar the focus correctly returns to the element that triggered it.

GITHUB ISSUE (Open Source Contributors)

NA

JIRA TASK (Eightfold Employees Only):

https://eightfoldai.atlassian.net/browse/ENG-133628

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

• pull branch down locally and start storybook (yarn storybook)
• go to Snackbar
• Set closable to true in the controls
• Verify if focus goes to the close button on snackbar.
• Verify if focus returns back to the element that triggered it.

case 1] snackbar triggerd when input is incorrect

Screen.Recording.2025-03-25.at.2.50.50.PM.mov

case2] snackbar triggered on button click.

Screen.Recording.2025-03-25.at.3.08.43.PM.mov

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[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.42%. Comparing base (7eeb006) to head (bfc3285).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/Snackbar/snack.ts	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #970      +/-   ##
==========================================
- Coverage   84.44%   84.42%   -0.02%     
==========================================
  Files        1104     1104              
  Lines       20613    20615       +2     
  Branches     7807     7809       +2     
==========================================
- Hits        17406    17405       -1     
- Misses       3119     3122       +3     
  Partials       88       88              

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