Bug 249791

It's time to start making breaking changes for the WPE 2.0 API version, but we cannot actually do this currently because our ENABLE_COG option depends on an external checkout of cog that already depends on WPE 2.0. Removing API that cog uses results in WPE port build failure. But we also cannot plausibly change cog to use new APIs that do not yet exist in WebKit because we cannot commit them because we have not yet updated cog. Aaah, it's circular!

I see two workable options:

 1. WebKit must depend on side branches of cog, where cog is modified to account for WebKit API changes that have not yet landed in WebKit
 2. Simply turn off ENABLE_COG for now, and reenable right before releasing 2.39.90 when the API stabilizes

My preference is option 2 because that would be easier for WebKit development, although it risks that we forget to keep cog in good shape. We'll want to remember to turn cog on again in February when the API is frozen.