Added "_path" and "_name" properties to ObjPathProxy

[tran-simon]

This adds the ability to get the path of the ObjPathProxy object without having to use the "getPath" function every time.

Exemple:

interface IExample extends ObjPath {
  one: number;
  two: string;
  nested: IExample;
  collection: IExample[];
}
const p = createProxy<IExample>();
console.log(p.one._path); //  'one'
console.log(p.nested.collection[2].one._path); //'nested/collection/2/one'
console.log(p.one._name); //  'one'
console.log(p.nested.collection[2].one._name); //'one'

[Taras-Tymchiy]

I'd suggest using Symbols instead of underscored prop names. This would also make them private.

[Taras-Tymchiy]

Removing those functions makes this lib incompatible with previous version. That would be a breaking change.
If the reason of adding the _path prop was to cache path instead of computing it every time, I'd suggest returning the _path value in the getPath function

[Taras-Tymchiy]

Hello Simon!
Thank you for spending your time on making this PR. I appreciate it!
I left a few suggestions in the inline comments.