Array buffer asset item

[takahirox]

Description:

This PR adds responseType attribute to a-asset-item.
It's necessary for THREE.GLTFLoader in r84. #2378
And it'll be helpful for user components which need arraybuffer data.

It has a limitation.
If we attempt to load the same data as different responseTypes,
only the responseType of the first attempt is applied
because it loads from cache if exists.

I think it won't cause any problems because
there's no situation that we wanna load the same data with different responseTypes.
(If exists, let me know.)

Changes proposed:

• Add responseType attribute to a-asset-item.
• Add responseType tests

[ngokevin]

fileLoader.setResponseType(this.getAttribute('response-type') || 'text');

html attribute case insensitive

[takahirox]

Oops, thanks! I'll update.

[ngokevin]

I've added docs and made the quick update. Thanks!

[takahirox]

Thanks for the update!

I have a question.

You changed the order of

THREE.Cache.remove(XHR_SRC);
var assetItem = document.createElement('a-asset-item');

Is there any special reasons you needed to change?
And if so, we should change the order here, too?

aframe/tests/core/a-assets.test.js

Line 276 in 3c074bd

THREE.Cache.remove(XHR_SRC);