Stop returning NOTCAPABLE errors from WASI calls. (#4666)

* Stop returning `NOTCAPABLE` errors from WASI calls.

`ENOTCAPABLE` was an error code that is used as part of the rights
system, from CloudABI. There is a set of flags associated with each file
descriptor listing which operations can be performed with the file
descriptor, and if an attempt is made to perform an operation with a
file descriptor that isn't permitted by its rights flags, it fails with
`ENOTCAPABLE`.

WASI is removing the rights system. For example, WebAssembly/wasi-libc#294
removed support for translating `ENOTCAPABLE` into POSIX error codes, on
the assumption that engines should stop using it.

So as another step to migrating away from the rights system, remove uses
of the `ENOTCAPABLE` error.

* Update crates/wasi-common/src/file.rs

Co-authored-by: Jamey Sharp <jamey@minilop.net>

* Update crates/wasi-common/src/dir.rs

Co-authored-by: Jamey Sharp <jamey@minilop.net>

Co-authored-by: Jamey Sharp <jamey@minilop.net>

crates/wasi-common/src/file.rs

@@ -238,7 +238,16 @@ impl FileEntry {
         if self.caps.contains(caps) {
             Ok(())
         } else {
-            Err(Error::not_capable().context(format!("desired {:?}, has {:?}", caps, self.caps,)))
+            let missing = caps & !self.caps;
+            let err = if missing.intersects(FileCaps::READ | FileCaps::WRITE) {
+                // `EBADF` is a little surprising here because it's also used
+                // for unknown-file-descriptor errors, but it's what POSIX uses
+                // in this situation.
+                Error::badf()
+            } else {
+                Error::perm()
+            };
+            Err(err.context(format!("desired rights {:?}, has {:?}", caps, self.caps)))
         }
     }