fix(react-avatar): prevent spreading of custom props on html element

[dmytrokirpa]

This pull request addresses a bug in the @fluentui/react-avatar package to prevent custom props from being incorrectly spread onto HTML elements, and adds tests to ensure correct prop handling and slot logic. Also adjusted the logic for setting the default icon in useAvatar_unstable so that it only assigns the default icon if the children property is not explicitly provided, allowing the default icon to be removed when desired

[github-actions]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-avatar Avatar	48.479 kB 15.359 kB	48.474 kB 15.374 kB	-5 B 15 B
react-avatar AvatarGroupItem	61.867 kB 19.384 kB	61.862 kB 19.402 kB	-5 B 18 B
react-components react-components: entire library	1.3 MB 324.941 kB	1.3 MB 324.957 kB	-5 B 16 B
react-headless-components-preview react-headless-components-preview: entire library	64.854 kB 19.302 kB	64.858 kB 19.318 kB	4 B 16 B
react-persona Persona	55.434 kB 17.299 kB	55.429 kB 17.308 kB	-5 B 9 B

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
react-avatar AvatarGroup	17.482 kB 7.002 kB
react-components react-components: Button, FluentProvider & webLightTheme	70.397 kB 19.96 kB
react-components react-components: Accordion, Button, FluentProvider, Image, Menu, Popover	237.187 kB 68.891 kB
react-components react-components: FluentProvider & webLightTheme	43.612 kB 14.022 kB
react-portal-compat PortalCompatProvider	8.386 kB 2.624 kB
react-table DataGrid	159.783 kB 45.012 kB
react-table Table (Primitives only)	40.997 kB 13.172 kB
react-table Table as DataGrid	131.005 kB 36.012 kB
react-table Table (Selection only)	69.391 kB 19.404 kB
react-table Table (Sort only)	68.034 kB 19.022 kB
react-tag-picker @fluentui/react-tag-picker - package	187.178 kB 55.977 kB
react-tags InteractionTag	13.724 kB 5.47 kB
react-tags Tag	29.648 kB 9.429 kB
react-tags TagGroup	82.247 kB 24.152 kB
react-timepicker-compat TimePicker	108.977 kB 36.038 kB
react-tree FlatTree	148.099 kB 42.211 kB
react-tree PersonaFlatTree	149.927 kB 42.585 kB
react-tree PersonaTree	145.987 kB 41.411 kB
react-tree Tree	144.165 kB 41.037 kB

_{🤖 This report was generated against a90fad387b40614102e9bc9c93c822c2ab1e81ee}

[github-actions]

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