WebExtBrowserCompatTable macro should support "alternative_name"

[wbamberg]

This PR: mdn/browser-compat-data#263 uses alternative_name, which the WebExtension table macro doesn't support.

Note that at some point we expect a new macro to be ready, that will work for all MDN pages (i.e. JS and CSS as well as WebExtensions) and at that point we will switch over to that table. So depending on when that will happen, it might be better to wait, than to fix this now.

[Elchi3]

Note that at some point we expect a new macro to be ready, that will work for all MDN pages

This has happened. compat.ejs is the single compat table implementation and webext macros route through it now. ({{compat}} will be changed again for the redesigned compat tables, but alternative_name should be available then, too).