Add HC styling for Switch when using font icons

[tomi-msft]

This PR fixes a visual issue with the Switch component in HC mode when the icon rendered is a font icon. The <i> tag has a black backplate in HC mode that doesn't get overridden by the color of its parent.

Fixes #31192

[fabricteam]

Perf Analysis (@fluentui/react-components)

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
FluentProviderWithTheme	virtual-rerender	34	41	10	Possible regression

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
Avatar	mount	602	627	5000
Button	mount	315	306	5000
Field	mount	1098	1129	5000
FluentProvider	mount	720	693	5000
FluentProviderWithTheme	mount	83	83	10
FluentProviderWithTheme	virtual-rerender	34	41	10	Possible regression
FluentProviderWithTheme	virtual-rerender-with-unmount	76	75	10
MakeStyles	mount	845	862	50000
Persona	mount	1765	1723	5000
SpinButton	mount	1357	1358	5000
SwatchPicker	mount	1534	1552	5000

[codesandbox-ci[bot]]

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[fabricteam]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-components react-components: entire library	1.098 MB 266.601 kB	1.098 MB 266.626 kB	148 B 25 B
react-switch Switch	35.14 kB 11.199 kB	35.288 kB 11.226 kB	148 B 27 B

Unchanged fixtures

| Package & Exports | Size (minified/GZIP) | | ----------------- | -------------------: | | react-components
react-components: Button, FluentProvider & webLightTheme | `71.104 kB`
`20.52 kB` | | react-components
react-components: Accordion, Button, FluentProvider, Image, Menu, Popover | `221.203 kB`
`62.464 kB` | | react-components
react-components: FluentProvider & webLightTheme | `43.591 kB`
`14.356 kB` | | react-portal-compat
PortalCompatProvider | `7.944 kB`
`2.588 kB` |

_{🤖 This report was generated against 05aa0d7e44ec602ca2a6a3a5303603d39d6844bb}

[fabricteam]

🕵 fluentuiv9 No visual regressions between this PR and main

[behowell]

When checking the PR demo site, I noticed that the switch disappears on mouse down. But that bug also repros before this change, so I logged a separate issue about it:

• https://github.com/microsoft/fluentui/issues/31244