refactor: comment M.path.is_descendant to prepare deperecation in future

We don't deprecate it currently as the suggested replacement
(vim.fs.relpath) isn't available on the minimum supported neovim
version.

Work on #2079.

lua/lspconfig/util.lua

@@ -95,57 +95,6 @@ function M.create_module_commands(module_name, commands)
   end
 end
 
--- Some path utilities
-M.path = (function()
-  --- @param path string
-  --- @return boolean
-  local function is_fs_root(path)
-    if iswin then
-      return path:match '^%a:$'
-    else
-      return path == '/'
-    end
-  end
-
-  -- Traverse the path calling cb along the way.
-  local function traverse_parents(path, cb)
-    path = vim.loop.fs_realpath(path)
-    local dir = path
-    -- Just in case our algo is buggy, don't infinite loop.
-    for _ = 1, 100 do
-      dir = vim.fs.dirname(dir)
-      if not dir then
-        return
-      end
-      -- If we can't ascend further, then stop looking.
-      if cb(dir, path) then
-        return dir, path
-      end
-      if is_fs_root(dir) then
-        break
-      end
-    end
-  end
-
-  local function is_descendant(root, path)
-    if not path then
-      return false
-    end
-
-    local function cb(dir, _)
-      return dir == root
-    end
-
-    local dir, _ = traverse_parents(path, cb)
-
-    return dir == root
-  end
-
-  return {
-    is_descendant = is_descendant,
-  }
-end)()
-
 function M.search_ancestors(startpath, func)
   if nvim_eleven then
     validate('func', func, 'function')
@@ -294,7 +243,52 @@ function M.strip_archive_subpath(path)
   return path
 end
 
---- Functions that can be removed once minimum required neovim version is high enough
+--- Public functions that can be deprecated once minimum required neovim version is high enough
+
+--- This can be replaced with `vim.fs.relpath` once minimum neovim version is at least 0.11.
+function M.path.is_descendant(root, path)
+  local function is_fs_root(_path)
+    if iswin then
+      return _path:match '^%a:$'
+    else
+      return _path == '/'
+    end
+  end
+
+  -- Traverse the path calling cb along the way.
+  local function traverse_parents(_path, cb)
+    _path = vim.loop.fs_realpath(_path)
+    local dir = _path
+    -- Just in case our algo is buggy, don't infinite loop.
+    for _ = 1, 100 do
+      dir = vim.fs.dirname(dir)
+      if not dir then
+        return
+      end
+      -- If we can't ascend further, then stop looking.
+      if cb(dir, _path) then
+        return dir, _path
+      end
+      if is_fs_root(dir) then
+        break
+      end
+    end
+  end
+
+  if not path then
+    return false
+  end
+
+  local function cb(dir, _)
+    return dir == root
+  end
+
+  local dir, _ = traverse_parents(path, cb)
+
+  return dir == root
+end
+
+--- Helper functions that can be removed once minimum required neovim version is high enough
 
 function M.tbl_flatten(t)
   --- @diagnostic disable-next-line:deprecated