Add a way to append a component to `NodePath`

[timothyqiu]

Describe the project you are working on

An in-game inspector.

Describe the problem or limitation you are having in your project

When trying to build a NodePath from Tree hierarchy, I found that NodePath API is lacking.

var path := ^"Hello"

# You can't do any of this currently.
path = path.join("World")
path += "/World"

# It has to be converted to String, changed, then converted to NodePath again.
path = str(path).path_join("World")
path = str(path) + "/World"

NodePath stores path components as a vector. Converting it to a string involves string concatenation.

It's a waste converting back and forth for appending a component to the path.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add APIs for NodePath manipulation.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

var path := ^"Hello"

# Add operator+ to append a NodePath / StringName / String
var another := ^"World"
another += path
# `another` is now `World/Hello`
# operator+ acts the same as `join()` described below

# Use `join()` to append a NodePath / StringName / String
path.join("World")
# Hello/World

# If conditions permit, support for variadic arguments may also be provided.
path.join("foo", "bar", "baz")
# Hello/foo/bar/baz

If this enhancement will not be used often, can it be worked around with a few lines of script?

No.

Is there a reason why this should be core and not an add-on in the asset library?

Core API related.