This commit tweaks WebIDL expansion of the "long long" and "unsigned long long"
types to expand to a union of an 32-bit integer and a double. This reflects how
almost none of the APIs on the web today actually work with a `BigInt` (what the
previous Rust type of `i64` translates to) and how JS itself fundamentally
operates with these APIs.
Eventually this may not be necessary if we can natively connect to C++ engines
with the `i64` type, but until that day comes this should provide more useful
interfaces as they shoudl work in all browsers.
Closes#800
This commit moves the `webidl/tests` folder to a new `crates/webidl-tests` crate
(to have a test-only build script) and ports them to the `#[wasm_bindgen_test]`
attribute, which should hopefully make testing much speedier for execution!
