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.

Cargo.lock

@@ -3129,6 +3129,7 @@ version = "0.33.0"
 dependencies = [
  "anyhow",
  "async-trait",
+ "atty",
  "cap-fs-ext",
  "cap-rand",
  "cap-std",