* Support parsing the text format in `wasmtime` crate
This commit adds support to the `wasmtime::Module` type to parse the
text format. This is often quite convenient to support in testing or
tinkering with the runtime. Additionally the `wat` parser is pretty
lightweight and easy to add to builds, so it's relatively easy for us to
support as well!
The exact manner that this is now supported comes with a few updates to
the existing API:
* A new optional feature of the `wasmtime` crate, `wat`, has been added.
This is enabled by default.
* The `Module::new` API now takes `impl AsRef<[u8]>` instead of just
`&[u8]`, and when the `wat` feature is enabled it will attempt to
interpret it either as a wasm binary or as the text format. Note that
this check is quite cheap since you just check the first byte.
* A `Module::from_file` API was added as a convenience to parse a file
from disk, allowing error messages for `*.wat` files on disk to be a
bit nicer.
* APIs like `Module::new_unchecked` and `Module::validate` remain
unchanged, they require the binary format to be called.
The intention here is to make this as convenient as possible for new
developers of the `wasmtime` crate. By changing the default behavior
though this has ramifications such as, for example, supporting the text
format implicitly through the C API now.
* Handle review comments
* Update more tests to avoid usage of `wat` crate
* Go back to unchecked for now in wasm_module_new
Looks like C# tests rely on this?
This continues #788 and literally removes the type from the public API
of the `wasmtime` crate, making it inaccessible to the outside world.
Now it's purely an implementation detail, yay!
* Only require `str` in `new_with_name`
It's a bit more idiomatic to have APIs require `&str` rather than
`String`, and the allocation doesn't matter much here since creating a
`Module` is pretty expensive anyway.
* Update a test
