[core] fix(RangeSlider): render handle correctly on first mount in popover

[adidahiya]

Fixes #4417

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

Update DOM measurement code to use element.offsetWidth and element.offsetHeight to get an accurate DOMRect for the handle element.

Credit to @pgoldberg for diving in to diagnose the issue and coming up with this potential solution 👍🏽

Reviewers should focus on:

No regressions in Slider & RangeSlider behavior

Screenshot

Without the implementation change:

After adjusting to use offsetWidth and offsetHeight:

[adidahiya]

[core] fix(RangeSlider): render handle correctly on first mount in popover

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.