Dialog API: Support MIME types?

[Semphriss]

I've been reading the JS File System API for Emscripten support, and I noticed it uses MIME types. The potential fallbacks using <input type-"file" /> also work with MIME. I believe the same may apply for some other platforms. Would it be worth checking to add a place for them in file filters?

[icculus]

I don't have an opinion on this at the moment, but I'm tossing this into 3.0 ABI milestone so we don't forget to look at this.

[slouken]

Since this isn't generally supported across platforms, let's not do this for now. We can add it later if we decide it's important.