[Task] Update the Query Parser to be able to parse to AST and plain JSON with ObjectId

Currently the ObjectID is encoded as a simple string (hexadecimal) and decoded as a string too.
This force us to navigate through the entire json object and try to parse every string into a ObjectId.

We want to change this for performance reason to encode the ObjectId as a specific string "ObjectId(xxxx)" and decode as a BSON.ObjectId (with elixir-bson

What should be done

The parser should be able to parse a String into a JSON object or an AST tree that represent the query.
Currently, the parser only parse into AST.
In both case, the parser should decode the ObjectID correctly.

Example :

str = "{\"_id\": \"ObjectId(12345abcd)\"}"
}
Parser.json(str)
> %{"_id" => #ObjectId{ref: "12345abcd"}}

Start with the existing parser entry point and the Parser.json(str) API described in the issue, then trace how the current AST output is produced. The work is done when parsing supports both a JSON object and an AST tree, and the ObjectId(xxxx) representation decodes to BSON.ObjectId rather than a plain string.