fix: fixing breadcrumb spacing

[williamw2]

Description

Updating breadcrumb spacing per design guidance. Reducing padding around breadcrumb separator from 8px to 4px.

I investigated replacing the custom breadcrumb markup in the form with the FASTComponent Breadcrumb controls, however, this would require refactoring that will be tackled as part of the larger effort to rebuild the fast-tooling-react package in web components.

Motivation & context

Fixes: #2043

Issue type checklist

• Chore: A change that does not impact distributed packages.
• Bug fix: A change that fixes an issue, link to the issue above.
• New feature: A change that adds functionality.

Is this a breaking change?

• This change causes current functionality to break.

Adding or modifying component(s) in @microsoft/fast-components checklist

• I have added a new component
• I have modified an existing component
• I have updated the definition file
• I have updated the configuration file

Process & policy checklist

• 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.