Migrate os calls to pathlib calls in hardlink util function

See discussion here: #5684 (comment)

Author: alch-emi

beets/util/__init__.py

@@ -578,12 +578,16 @@ def hardlink(path: bytes, dest: bytes, replace: bool = False):
     if samefile(path, dest):
         return
 
-    if os.path.exists(syspath(dest)) and not replace:
+    # Dereference symlinks, expand "~", and convert relative paths to absolute
+    origin_path = Path(os.fsdecode(path)).expanduser().resolve()
+    dest_path = Path(os.fsdecode(dest)).expanduser().resolve()
+
+    if dest_path.exists() and not replace:
         raise FilesystemError("file exists", "rename", (path, dest))
     try:
-        # This step dereferences any symlinks and converts to an absolute path
-        resolved_origin = Path(syspath(path)).resolve()
-        os.link(resolved_origin, syspath(dest))
+        os.link(origin_path, dest_path)
+        # When support for Python 3.9 is dropped, this can be replaced with:
+        # dest_path.hardlink_to(origin_path)
     except NotImplementedError:
         raise FilesystemError(
             "OS does not support hard links.link",