Add Vec3 Support for setFromEulerAngles() pc.Quat function

[zishiwu123]

Fixes #3663

Discussion
I thought of two ways to instantiate ex, ey, and ez given the condition where ex instanceof Vec3 is true:

1. Small premature optimization by setting ex = ex.x last so we don't have to make a clone of ex. A rule of thumb in software development is that "premature optimization is the root of all evil". However, I think it is okay to bend the rules in this situation since this is a game engine where performance matters. If a reviewer says otherwise, I will make changes based on their suggestions.

if (ex instanceof Vec3) {
    ez = ex.z;
    ey = ex.y;
    ex = ex.x;
}

2. Clone ex and use the cloned Vec3 to instantiate ex, ey, and ez. Depending on the person, this option might be easier to understand than option 1. But there is a small performance penalty because this creates an extra Vec3 object.

if (ex instanceof Vec3) {
    const v = ex.clone();
    ex = v.x;
    ey = v.y;
    ez = v.z;
}

I confirm I have read the contributing guidelines and signed the Contributor License Agreement.

[Maksims]

No need to clone (it will lead to memory allocations, which then lead to minor/major GC stalls).
Code like this I believe is fine too, which eliminates the potential issue of someone changing the order of lines.

if (ex instanceof Vec3) {
    const vec = ex;
    ex = vec.x;
    ey = vec.y;
    ez = vec.z;
}

Also, it makes ey and ez function arguments optional.

[zishiwu123]

Good idea @Maksims . Compound values are assigned by reference in JavaScript so it would not create a new copy of the object. Plus it's safer because the order in which ex, ey, and ez are assigned doesn't matter in your idea.

[kungfooman]

Maybe simplify these four cases in GraphNode with this PR then:

https://github.com/playcanvas/engine/blob/main/src/scene/graph-node.js#L918

https://github.com/playcanvas/engine/blob/main/src/scene/graph-node.js#L1142

https://github.com/playcanvas/engine/blob/main/src/scene/graph-node.js#L1552

https://github.com/playcanvas/engine/blob/main/src/scene/graph-node.js#L1591

[zishiwu123]

@kungfooman Good idea. I pushed another commit in this PR based on your suggestion.

[kungfooman]

@kungfooman Good idea. I pushed another commit in this PR based on your suggestion.

Why still check if its a Vec3, can't you just simplify the code completely now (removing all those instanceof lines)? By just always passing x, y, z to Quat#setFromEulerAngles and let only that method check if its a Vec3

Not sure if I'm missing something, I didn't test it. Good job!

[zishiwu123]

@kungfooman Another good point. The instanceof check in the 4 lines you mentioned are redundant. I removed them and the tests still pass.

[willeastcott]

This is great - thanks!! 🙏