Add BRP method to mutate a component

[purplg]

Objective

Add a method to mutate components with BRP.

Currently the only way to modify a component on an entity with BRP is to insert a new one with the new values. This isn't ideal for several reasons, one reason being that the client has to know what all the fields are of the component and stay in sync with the server.

Solution

Add a new BRP method called bevy/mutate_component to mutate a single field in a component on an entity.

Testing

• Tested on a simple scene on all Transform and Name fields.
• Need to do more testing on other component types.

---

Showcase

Example JSON-RPC request to change the Name of an entity to "New name!"

{
    "jsonrpc": "2.0",
    "id": 0,
    "method": "bevy/mutate_component",
    "params": {
        "entity": 4294967308,
        "component": "bevy_ecs::name::Name",
        "path": ".name",
        "value": "New name!"
    }
}

[purplg]

I'm not sure what the convention is for multiple words in a method name is. Should the method be named differently? I'm trying to consider future methods for modifying other things like Resource's.

I had a few other ideas for methods:

• bevy/modify/component
• bevy/mutate/component
• bevy/component_mut this feels too Rusty in this context

[purplg]

I feel like the method handler could probably be done better or maybe in less steps. Any pointers here would be appreciated.