Fix isatty in WASI. (#3696)

WASI doesn't have an `isatty` ioctl or syscall, so wasi-libc's `isatty`
implementation uses the file descriptor type and rights to determine if
the file descriptor is likely to be a tty. The real fix here will be to
add an `isatty` call to WASI. But for now, have Wasmtime set the
filetype and rights for file descriptors so that wasi-libc's `isatty`
works as expected.

crates/wasi-common/tokio/src/file.rs

@@ -112,6 +112,9 @@ macro_rules! wasi_file_impl {
             async fn num_ready_bytes(&self) -> Result<u64, Error> {
                 block_on_dummy_executor(|| self.0.num_ready_bytes())
             }
+            fn isatty(&self) -> bool {
+                self.0.isatty()
+            }
 
             #[cfg(not(windows))]
             async fn readable(&self) -> Result<(), Error> {