refactor(Collapse): streamline atom functions

[robertpenner]

Previous Behavior

• Duplication in enter/exit implementations in atom functions:
  • opacity
  • whitespace
• No fade atom function in common location

New Behavior

• Duplication factored out
• fadeAtom is in a common location and Collapse imports it for reuse
• Added comments and explanatory types as needed

Future Work

• Use fadeAtom in other motion components wherever possible
  • MessageBarGroup.motions.tsx copies fadeAtom code; it can import it instead, after this PR.

Related Issue(s)

• Fixes [Collapse] Streamline motion atom functions #33636

[github-actions]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-accordion Accordion (including children components)	107.08 kB 32.786 kB	106.922 kB 32.796 kB	-158 B 10 B
react-components react-components: Accordion, Button, FluentProvider, Image, Menu, Popover	222.703 kB 64.42 kB	222.545 kB 64.43 kB	-158 B 10 B
react-components react-components: entire library	1.164 MB 291.232 kB	1.164 MB 291.242 kB	-158 B 10 B
react-toast Toast (including Toaster)	101.371 kB 30.477 kB	101.213 kB 30.472 kB	-158 B -5 B
react-tree FlatTree	145.462 kB 41.771 kB	145.302 kB 41.779 kB	-160 B 8 B
react-tree PersonaFlatTree	146.15 kB 41.881 kB	145.99 kB 41.89 kB	-160 B 9 B
react-tree PersonaTree	142.381 kB 40.703 kB	142.222 kB 40.708 kB	-159 B 5 B
react-tree Tree	141.693 kB 40.602 kB	141.534 kB 40.606 kB	-159 B 4 B

Unchanged fixtures

Package & Exports	Size (minified/GZIP)
react-components react-components: Button, FluentProvider & webLightTheme	69.21 kB 20.174 kB
react-components react-components: FluentProvider & webLightTheme	44.447 kB 14.59 kB
react-dialog Dialog (including children components)	100.417 kB 30.097 kB
react-message-bar MessageBar (all components)	24.825 kB 9.267 kB
react-portal-compat PortalCompatProvider	8.39 kB 2.64 kB
react-timepicker-compat TimePicker	108.525 kB 36.087 kB

_{🤖 This report was generated against e561700253aaaf2c6e17e5c70bf10c12c434bd96}

[github-actions]

Pull request demo site: URL