Add typed array utility functions

[richarddd]

Expose a few utility functions to check and create typed arrays. Also add JS_NewTypedArray from upstream.

Fixes #758

[chqrlie]

I really don't like this approach: instead of 12 more APIs, I suggest a generic extensible method.

[saghul]

IsTupedArray with the enum? That works too.

[richarddd]

@saghul @chqrlie OK to merge now?

[saghul]

One minor nit, LGTM otherwise!

[saghul]

@chqrlie Any further comments?

[chqrlie]

@chqrlie Any further comments?

Aside from the remark about the obscure code in JS_GetTypedArrayType, there is a gotcha in the published enum: JS_TYPED_ARRAY_FLOAT16 in the published API is before JS_TYPED_ARRAY_FLOAT32, which seems logical, but makes the last 2 enum values incompatible with the enum published in bellard/quickjs.

If we keep this logical ordering, I will have to break backward compatibility when backporting the float16 support.

I cannot measure if this may be a problem or not, @saghul and @bnoordhuis what is your experience?

[saghul]

I'd say that's ok but I wouldn't mind moving it around either.

[chqrlie]

I'd say that's ok but I wouldn't mind moving it around either.

@bnoordhuis what is your take on this?

[bnoordhuis]

I'd say it's fine to keep it the way it is. We're not promising AP/ABI stability just yet.