[Grid] Fix breakpoints not working with fractional pixels

[hksalessio]

Pull Request

📖 Description

I noticed that the FluentGrid component displayed grid items that were meant to be hidden at fractional pixel sizes.
For example, the FluentCard labeled 'xs="12" sm="6" Hidden="SmAndDown"' in following screenshot is hidden with a browser size '<= 599px' or '>= 600px and <= 959px' but not inbetween those values (i.e. 599.33px):

To fix this, I added .98px to the max-width breakpoints, as explained under following link:
https://stackoverflow.com/questions/54596219/why-do-some-max-width-media-queries-use-a-98px

✅ Checklist

General

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Component-specific

• I have added a new component
• I have added Unit Tests for my new compontent
• I have modified an existing component
• I have validate Unit Tests for an existing component

[vnbaaij]

Looks good to me!