path_get refactor and implementation of missing path_ hostcalls on Windows (#41)

* Move path_get outside of sys module

* Add implementation of readlinkat

* Clean up path_open; use OpenOptions as much as possible

* Enable close_preopen test

* Implement path_create_directory; fix path_open

* Refactor path concatenation onto a descriptor

* Implement path_remove_directory

* Implement path_unlink_file

* Rewrite path_open using specific access mask

* Fix error mapping when unlinking file

* Fix readlinkat to pass nofollow_errors testcase

* Clean up winerror to WASI conversion

* Spoof creating dangling symlinks on windows (hacky!)

* Add positive testcase for readlink

* Implement path_readlink (for nonzero buffers for now)

* Clean up

* Add Symlink struct immitating *nix symlink

* Fix path_readlink

* Augment interesting_paths testcase with trailing slashes example

* Encapsulate path_get return value as PathGet struct

* Remove dangling symlink emulation

* Extract dangling symlinks into its own testcase

This way, we can re-enable nofollow_errors testcase
on Windows also.

* Return __WASI_ENOTCAPABLE if user lacks perms to symlink

winx/src/winerror.rs

@@ -78,6 +78,12 @@ win_error_expand! {
     ERROR_INVALID_NAME,
     /// The process cannot access the file because it is being used by another process.
     ERROR_SHARING_VIOLATION,
+    /// A required privilege is not held by the client.
+    ERROR_PRIVILEGE_NOT_HELD,
+    /// The file or directory is not a reparse point.
+    ERROR_NOT_A_REPARSE_POINT,
+    /// An attempt was made to move the file pointer before the beginning of the file.
+    ERROR_NEGATIVE_SEEK,
 }
 
 impl WinError {