Add buffer data capture and buffer data view

[Emily-TTG]

[Note that this pretty much requires the application to startCapture manually so that buffer uploads are actually seen]

Add functionality to capture buffer contents and allow their viewing via. the relevant draw call -- similar to Renderdoc's buffer/resource view functionality. Formats the buffer by the bound attributes at draw time to keep things nice and readable.

In future it might be nice to also support WebGL2 buffer readback for getting pre-record buffer data but this WebGL1 impl is more of a catchall initial impl.

My actual frontend skills aren't great so if there's something wrong with the visual design I've left Allow edits by maintainers on.

New button on draw call view:

[sebavan]

Can you limit the buffer capture to the first few elements ? let s say 16 ?

[Emily-TTG]

@sebavan that seems like it'd kind of defeat the purpose of having a buffer view no? I can add a setting to limit the max capture length but I was just following the RenderDoc pattern of "capture everything". Would it be preferable that go into extension settings with an override in the spector object or?

[sebavan]

Capturing the buffers was asked to not be present by a few websites in the past. It might not be relevant anymore but I recall they were people scared by such an easy access to their full meshes:

#294

[Emily-TTG]

I suppose? Could the application maybe require an opt-in on it then via ._allowBufferCapture or similar on the context object -- so websites that don't want stuff yoinked can't easily be scraped without some extra work to inject JS.

I do appreciate this is a concern -- RenderDoc kind of assuages it by just saying it's against the usage supported by the RenderDoc project but I can see how that might be flimsy.