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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