* Change the name of wit-bindgen's host implementation traits.
Instead of naming the host implementation trait something like
`wasi_filesystem::WasiFilesystem`, name it `wasi_filesystem::Host`, and
avoid using the identifier `Host` in other places.
This fixes a collision when generating bindings for the current
wasi-clock API, which contains an interface `wall-clock` which contains
a type `wall-clock`, which created a naming collision on the name
`WallClock`.
* Update tests to use the new trait name.
* Fix one more.
* Add the new test interface to the simple-wasi world.
This commit fixes a bug in the `bindgen!` macro for components where
previously the `param` and `result` properties weren't properly
calculated depending on the structure of the type and which types were
visited in which order. This is simplified to use a `LiveTypes`
structure from the `wit-parser` crate and relies on that to do necessary
recursion.
