Re: [img-conversion] canDecodeType \ canEncodeType could be supports() (#12)

It's fine to have just "image/whatever"... we just don't want to get into a situation where we end up with things like:

```
'image/vnd.microsoft.icon;format=bmp,bpp=32'
```
Or similar. 

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Reply to this email directly or view it on GitHub:
https://github.com/WICG/img-conversion/issues/12#issuecomment-142688323