Add WP 5.3 meta changes

[TimothyBJacobs]

WIP

[zanona]

hi @TimothyBJacobs , the only thing here is that the initial value for object meta type is still returned as an empty array rather than a JSON object.
As the initial value for number or integer types is 0, for a string, '', for both array and object types the REST API returns [] as opposed to [] and {} respectively.

[TimothyBJacobs]

👋 @zanona. Yeah this is tricky and is a problem across all of the REST API. We use associative arrays for objects, which as you pointed out get json encoded as []. We can't simply use JSON_FORCE_OBJECT because sometimes we have actual empty arrays.

I think we would need a post processing layer of some kind that checks against the schema and switches out empty arrays to an stdClass instance if that property is defined in the schema as an object.

If you have a chance, it'd be great to open a trac ticket for this issue.