ARROW-10042: [Rust] Don't compare ArrayData's Buffer's capacities

When computing equality for two `ArrayData` instances, the capacities of
the underlying `Buffer`s are not relevant.

rust/arrow/src/array/data.rs

@@ -270,7 +270,7 @@ fn compare_buffer_regions(
     let shorter_len = left.len().min(right.len());
     let s_sliced = left.bit_slice(left_offset, shorter_len);
     let o_sliced = right.bit_slice(right_offset, shorter_len);
-    s_sliced == o_sliced
+    s_sliced.data() == o_sliced.data()
 }
 
 /// Builder for `ArrayData` type