Fix path_open trailing slash edge case

`path_open` discards trailing slashes when path_open is creating a new
file.  This is a bug because trailing slash is semantically
meaningful. Other runtimes like WasmEdge, Wazero, WAMR, Wasmtime, and
Node correctly preserves the trailing slash.

fixes #4833

lib/wasix/src/syscalls/wasi/path_open.rs

@@ -304,6 +304,12 @@ pub(crate) fn path_open_internal(
             if o_flags.contains(Oflags::DIRECTORY) {
                 return Ok(Err(Errno::Notdir));
             }
+
+            // Trailing slash matters. But the underlying opener normalizes it away later.
+            if path.ends_with('/') {
+                return Ok(Err(Errno::Isdir));
+            }
+
             // strip end file name
 
             let (parent_inode, new_entity_name) =

tests/wasi-fyi/fs_open_trailing_slash.rs

@@ -14,14 +14,18 @@ extern "C" {
 }
 
 const ERRNO_SUCCESS: i32 = 0;
+const ERRNO_ISDIR: i32 = 31;
 const ERRNO_NOTDIR: i32 = 54;
+const OFLAGS_CREAT: i32 = 1;
 const RIGHTS_FD_READ: i64 = 2;
+const RIGHTS_FD_WRITE: i64 = 64;
 
 fn main() {
     unsafe {
         let fd = 5;
         let path_ok = "fyi/fs_open_trailing_slash.dir/file";
         let path_bad = "fyi/fs_open_trailing_slash.dir/file/";
+        let path_bad_new_file = "fyi/fs_open_trailing_slash.dir/new-file/";
         let errno = path_open(
             fd,
             0,
@@ -53,5 +57,21 @@ fn main() {
             errno, ERRNO_NOTDIR,
             "opening a regular file with a trailing slash should fail"
         );
+
+        let errno = path_open(
+            fd,
+            0,
+            path_bad_new_file.as_ptr() as i32,
+            path_bad_new_file.len() as i32,
+            OFLAGS_CREAT,
+            RIGHTS_FD_READ | RIGHTS_FD_WRITE,
+            0,
+            0,
+            1024,
+        );
+        assert_eq!(
+            errno, ERRNO_ISDIR,
+            "creating a regular file with a trailing slash should fail"
+        );
     }
 }