[ArrowStringArray] Use utf8_upper and utf8_lower functions from Apache Arrow (pandas-dev#41056)

Author: simonjayhawkins

pandas/core/arrays/string_arrow.py

@@ -757,3 +757,9 @@ def _str_map(self, f, na_value=None, dtype: Dtype | None = None):
             #    or .findall returns a list).
             # -> We don't know the result type. E.g. `.get` can return anything.
             return lib.map_infer_mask(arr, f, mask.view("uint8"))
+
+    def _str_lower(self):
+        return type(self)(pc.utf8_lower(self._data))
+
+    def _str_upper(self):
+        return type(self)(pc.utf8_upper(self._data))