Consider auto-generating CSS animation wrappers from CSSProperties.json

[Tim Nguyen (:ntim)]

I think this is worth doing, it's easy to forget to add animation support, so having fields in CSSProperties.json would help.

Since the most common type of animation are discrete ones, we should support:

```
"animation": "discrete",
```

but for more complex wrappers:

```
"animation": {
  "wrapper": "LengthPropertyWrapper",
  "flags": ["IsLengthPercentage", "NegativeLengthsAreInvalid"]
}
```

For custom wrappers:
```
"animation": {
  "wrapper": "PropertyWrapperFlex"
}
```

etc.

and then "animation": "not-animatable" if unsupported.

That field would be mandatory to add.

[Radar WebKit Bug Importer]

<rdar://problem/103781617>