docs(handbook): add icon docs to developer-handbook (#6300)
docs(handbook): add icon docs to developer-handbook (#6300)

* Update developer-handbook.md

* docs(handbook): add commands for snapshot changes

* docs(handbook): add breaking change notes for icons

Co-authored-by: TJ Egan <c8acf1a1b30b778f72fed9891301ce12a56d096c@gmail.com>
carbon-design-system/carbon-components,carbon-design-system/carbon-components,carbon-design-system/carbon-components