Add support for input streams to webaudio host

[mitchmindtree]

Currently the implementation panics with unimplemented!().

[kmaork]

Is this planned any time soon? Would you be able to help me if I were to implement this myself? @dpeckett @mitchmindtree

[sajattack]

I'm also interested in this feature, figured this issue could use a bump of expressed interest since it's sat for over 2 years.

[TheRealSeber]

Is there a strong reason behind why wasn't it still introduced? @mitchmindtree