Document a public API and SemVer policy (#7615)
Document a public API and SemVer policy (#7615)

* Document a "public API" and SemVer policy

* Apply copy edits from sideshowbarker

Co-authored-by: Michael[tm] Smith <a17fed27eaa842282862ff7c1b9c8395a26ac320@w3.org>

* Expand SemVer-protected WebExtension namespaces

Co-authored-by: Michael[tm] Smith <a17fed27eaa842282862ff7c1b9c8395a26ac320@w3.org>
mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data