preview 2 filesystem: allow stat on any opened fd

since file perms is now more accurately the file's access mode, a file
open for writing was having problems here.

in reality i dont think it makes sense to restrict this based on the
perms. if a file is opened, you should be able to stat it.

this fixes the path_link test, which was broken by prior changes.
additionally, this fix lets the path_open_dirfd_not_dir test pass.

crates/test-programs/tests/wasi-preview1-host-in-preview2.rs

@@ -233,7 +233,6 @@ async fn path_open_read_write() {
     run("path_open_read_write", true).await.unwrap()
 }
 #[test_log::test(tokio::test(flavor = "multi_thread"))]
-#[should_panic]
 async fn path_open_dirfd_not_dir() {
     run("path_open_dirfd_not_dir", true).await.unwrap()
 }

crates/wasi/src/preview2/preview2/filesystem.rs

@@ -352,16 +352,12 @@ impl<T: WasiView> filesystem::Host for T {
         let table = self.table();
         if table.is_file(fd) {
             let f = table.get_file(fd)?;
-            if !f.perms.contains(FilePerms::READ) {
-                return Err(ErrorCode::NotPermitted.into());
-            }
+            // No permissions check on stat: if opened, allowed to stat it
             let meta = f.file.metadata()?;
             Ok(descriptorstat_from(meta))
         } else if table.is_dir(fd) {
             let d = table.get_dir(fd)?;
-            if !d.perms.contains(DirPerms::READ) {
-                return Err(ErrorCode::NotPermitted.into());
-            }
+            // No permissions check on stat: if opened, allowed to stat it
             let meta = d.dir.dir_metadata()?;
             Ok(descriptorstat_from(meta))
         } else {