Add missing AbstractWritableDataStore base methods and arguments (pydata#10343)

Co-authored-by: Deepak Cherian <dcherian@users.noreply.github.com>

Author: sjperkins

xarray/backends/common.py

@@ -401,7 +401,10 @@ def encode_attribute(self, a):
         """encode one attribute"""
         return a
 
-    def set_dimension(self, dim, length):  # pragma: no cover
+    def prepare_variable(self, name, variable, check_encoding, unlimited_dims):
+        raise NotImplementedError()
+
+    def set_dimension(self, dim, length, is_unlimited):  # pragma: no cover
         raise NotImplementedError()
 
     def set_attribute(self, k, v):  # pragma: no cover