fix: SplitButton menuButton is at least 24px wide

[smhigley]

Previous Behavior

The menuButton was 23px wide by default, failing the new WCAG 2.2 minimum target size requirement by 1px.

New Behavior

The min-width of the menubutton is set to 24px for all sizes of splitbuttons. Toshie already got sign-off on the change (including for small splitbuttons) from partners, so we should be good to change the visuals.

[fabricteam]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-button SplitButton	49.93 kB 13.696 kB	49.933 kB 13.693 kB	3 B -3 B
react-components react-components: entire library	1.097 MB 270.919 kB	1.097 MB 270.917 kB	3 B -2 B

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
react-breadcrumb @fluentui/react-breadcrumb - package	113.699 kB 31.498 kB
react-button Button	37.104 kB 10.766 kB
react-button CompoundButton	43.518 kB 12.068 kB
react-button MenuButton	41.916 kB 12.119 kB
react-button ToggleButton	53.037 kB 12.528 kB
react-card Card - All	101.238 kB 28.624 kB
react-card Card	94.022 kB 26.806 kB
react-card CardFooter	14.355 kB 5.79 kB
react-card CardHeader	16.878 kB 6.666 kB
react-card CardPreview	14.42 kB 5.922 kB
react-components react-components: Button, FluentProvider & webLightTheme	69.14 kB 20.137 kB
react-components react-components: Accordion, Button, FluentProvider, Image, Menu, Popover	218 kB 63.151 kB
react-components react-components: FluentProvider & webLightTheme	44.447 kB 14.59 kB
react-dialog Dialog (including children components)	99.541 kB 29.849 kB
react-message-bar MessageBar (all components)	24.722 kB 9.205 kB
react-portal-compat PortalCompatProvider	8.39 kB 2.64 kB
react-tag-picker @fluentui/react-tag-picker - package	182.176 kB 54.779 kB
react-timepicker-compat TimePicker	107.387 kB 35.758 kB

_{🤖 This report was generated against 8492a7ebd12270b49dd3083671a859ada31b395b}

[fabricteam]

Perf Analysis (@fluentui/react-components)

No significant results to display.

All results

Scenario	Render type	Master Ticks	PR Ticks	Iterations	Status
Avatar	mount	644	611	5000
Button	mount	305	311	5000
Field	mount	1110	1148	5000
FluentProvider	mount	707	721	5000
FluentProviderWithTheme	mount	85	98	10
FluentProviderWithTheme	virtual-rerender	37	30	10
FluentProviderWithTheme	virtual-rerender-with-unmount	76	69	10
MakeStyles	mount	880	866	50000
Persona	mount	1764	1676	5000
SpinButton	mount	1397	1358	5000
SwatchPicker	mount	1647	1620	5000