refactor(Fade): migrate to new variant structure

[robertpenner]

Previous Behavior

• Fade motion component uses createPresenceComponentVariant to define variants.

New Behavior

• Fade motion component uses the new variant structure.

Related Issue(s)

• Fixes #33081

Tasks

• [x] 1. Migrate Fade's variant definitions to the functional style as in Collapse.
• [ ] 2. Update Fade's variant customization example in Storybook.

Future Work

• Migrate Scale's usage of createPresenceComponentVariant.
• Migrate unit tests that reference createPresenceComponentVariant and overridePresenceMotion.
• Delete createPresenceComponentVariant and overridePresenceMotion as unused and obsolete.

[fabricteam]

📊 Bundle size report

✅ No changes found

[fabricteam]

Perf Analysis (@fluentui/react-components)

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
FluentProviderWithTheme	virtual-rerender	34	46	10	Possible regression

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
Avatar	mount	631	657	5000
Button	mount	305	300	5000
Field	mount	1164	1187	5000
FluentProvider	mount	723	784	5000
FluentProviderWithTheme	mount	85	89	10
FluentProviderWithTheme	virtual-rerender	34	46	10	Possible regression
FluentProviderWithTheme	virtual-rerender-with-unmount	81	79	10
MakeStyles	mount	873	861	50000
Persona	mount	1731	1714	5000
SpinButton	mount	1401	1407	5000
SwatchPicker	mount	1677	1680	5000