Blender Git Loki

BlenLib: Add JSON Serialization/Deserialization Abstraction Layer.

Adds an abstraction layer to switch between serialization formats.
Currently only supports JSON. The abstraction layer supports
`String`, `Int`, `Array`, `Null`, `Boolean`, `Float` and `Object`. This
feature is only CPP complaint.

To write from a stream, the structure can be built by creating a value
(any subclass of `blender::io::serialize::Value` can do, and pass it to
the `serialize` method of a `blender::io::serialize::Formatter`. The
formatter is abstract and there is one implementation for JSON
(`JsonFormatter`).

To read from a stream use the `deserialize` method of the formatter.

{D12693} uses this abstraction layer to read/write asset indexes.

Reviewed By: Severin, sybren

Maniphest Tasks: T91430

Differential Revision: https://developer.blender.org/D12544