feat(datagrid): expose top index change event for virtual scroller

[valentin-mladenov]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• If applicable, have a visual design approval

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: CDE-2597

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[github-actions]

👋 @valentin-mladenov,

• 🙏 The Clarity team thanks you for opening a pull request
• 🎉 The build for this PR has succeeded
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• 🍿 In the meantime, view a preview of this PR
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Thank you,

🤖 Clarity Release Bot

[github-actions]

This PR introduces visual changes: 3ce4907
If these changes are intended and correct, please cherry-pick the above commit to this PR.

git checkout scrolling-based-on-top-visible-index
git fetch https://github.com/vmware-clarity/ng-clarity.git 3ce49077896ca6194d5c06533725f108de96f0e0
git cherry-pick 3ce49077896ca6194d5c06533725f108de96f0e0
git push

[valentin-mladenov]

related to #1719

[github-actions]

This PR introduces visual changes: b68045c
If these changes are intended and correct, please cherry-pick the above commit to this PR.

git checkout scrolling-based-on-top-visible-index
git fetch https://github.com/vmware-clarity/ng-clarity.git b68045ccdb5e2e20565dbe77d8b460fa32e18c8c
git cherry-pick b68045ccdb5e2e20565dbe77d8b460fa32e18c8c
git push