fix(side-panel): Parity work

[ruchas31]

Closes #8734

About Modal web component parity work

What did you change?

All points in the issue description are addressed except for:

• Animation points
• Action items - buttons to resize properly to fill the available area. The react component uses ActionSet utility and there is no such utility for WC so this will need to be developed separately. New issue created Sidepanel WC - Action items buttons do not display correctly #9139.
• Storybook: Missing feature flag option - the react component uses Resizer utility from carbon labs. This is not available in web component version. So this will need to be developed separately. New issue created Storybook: Sidepanel WC - Missing feature flag option for Resizer #9138.

How did you test and verify your work?

Storybook

PR Checklist

As the author of this PR, before marking ready for review, confirm you:

• Reviewed every line of the diff
• Updated documentation and storybook examples
• Wrote passing tests that cover this change
• Addressed any impact on accessibility (a11y)
• Tested for cross-browser consistency
• Validated that this code is ready for review and status checks should pass

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[codecov]

Codecov Report

❌ Patch coverage is 95.49550% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.77%. Comparing base (fec43b6) to head (a478783).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9136   +/-   ##
=======================================
  Coverage   76.77%   76.77%           
=======================================
  Files         490      490           
  Lines       21759    21855   +96     
  Branches     4676     4684    +8     
=======================================
+ Hits        16706    16780   +74     
- Misses       5053     5075   +22     

Components	Coverage Δ
ibm-products	76.83% <ø> (ø)
ibm-products-web-components	76.71% <95.49%> (+<0.01%)	⬆️

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