Loader: Add "setFromFetchOptions" function

[gkjohnson]

Related issue: --

Description

This is a suggestion to add a setFromFetchOptions( fetchOptions ) function to Loader. fetch has become the predominant way to perform requests and it comes with a (in my opinion) more intuitive set of options for defining the request that is not supported by the three.js loaders. In my apps I carry around a common fetch options object that defines the "mode", "credentials", and necessary "headers" needed to make a request for a certain set of resources and it's not immediately clear how to map those options to the old XMLHttpRequest / three.js Loader model. setFromFetchOptions makes it easy to map the more modern fetch options to those needed by the loader ultimately calling setWithCredentials, setCrossOrigin, and setRequestHeader with ( as far as I can tell) the equivalent values.

[Mugen87]

In my apps I carry around a common fetch options object that defines the "mode", "credentials", and necessary "headers" needed to make a request for a certain set of resources

You've made the PR based on this assumption but there are surely enough apps outside there which do not use such a workflow. Hence, setFromFetchOptions() seems to application specific to me and I would not add it to the generic Loader class.

[gkjohnson]

I never meant to imply this was more enabling for apps -- it's a convenience function that affords (in my opinion) a much more intuitive and ergonomic way to set request parameters on loaders and bring the API more up to par with the modern way to make requests (fetch).

At some point I'd think the FileLoader should be changed to use fetch under the hood (#22468) at which point using fetch options directly will be more natural.

[mrdoob]

At some point I'd think the FileLoader should be changed to use fetch under the hood (#22468) at which point using fetch options directly will be more natural.

That sounds good to me. And caniuse seems to be decent. Anyone wants to give it a go?

[gkjohnson]

Anyone wants to give it a go?

Maybe @DefinitelyMaybe is interested in converting FileLoader to use fetch instead of XMLHTTPRequest considering #22468?

[DefinitelyMaybe]

ooooooo, yeah, I'll look into it today