[css-display] Should all the inline-foo and inline foo forms be distinct? #1486

In #1246 we are provisionally deciding that inline-block and inline flow-root are syntactically distinct (for a legacy reason), so that they can blockify differently. This means that, in particular, writing display: inline flow-root and then asking for the computed value will give you inline flow-root. This no longer matches the other inline-ish values; in pairs like inline-flex/inline flex, they're equivalent, and writing either will get you inline-flex in the computed value (because it's the shortest version of the value).

So the additional question then is whether we're okay with inline-block/inline flow-root being the exception here. There are three options:

1. Leave inline-block/inline flow-root the only pair that is distinct in computed value. (Weird exception for legacy reasons.)
2. Make all the pairs distinct. (The only effect of this distinction in the other pairs is that they'll serialize differently in computed value.)
3. Revert [css-display] Blockification doesn't seem backwards-compatible for inline-blocks #1246 to the other option, so that inline-block/inline-flow-root are back to being identical, and both blockify to block flow. (This fails to preserve the flow-root-ness of inline flow-root, which might be unwanted.)