Enums should be alphabetized

Enums such as [those for `chrome.offscreen`](https://developer.chrome.com/docs/extensions/reference/offscreen/#type-Reason) are rendered in the same order they are entered into [the IDL source file](https://source.chromium.org/chromium/chromium/src/+/main:extensions/common/api/offscreen.idl). Rather than editing all source files to put enums in alphabetical order, we should just call a sorting function at the time the IDL is rendered as API reference.