Deprecate non-ComResult Results

[Rantanen]

I don't think there's much point in supporting custom results. One intended benefit for this was to support things like returning io::Result directly - but having the user do into() on that isn't asking too much more in the end.

Also given Microsoft is developing com-rs, I'm fine giving up on the "Intercom needs to be able to call any COM API" requirement and instead aim for "Most COM APIs but with the best ergonomics possible" and I feel requiring ComResult for fallible methods will give more benefits:

• We can remove #[infallible] and instead assume that any method that doesn't return ComResult should be considered #[infallible].
• We might be able to target stable Rust. The error traits are one of the only ones that require specialization currently.
• With stricter types, it should be easier to figure APIs for supporting custom error info when serializing into ComError.