Cleanup: Use switch and BLI_assert_unreachable() more.

Replace some `if/else if` chains by proper `switch` statement.

Replace some `BLI_assert(0)` calls by `BLI_assert_unreachable()` ones.

source/blender/blenlib/intern/array_utils.c

@@ -53,7 +53,7 @@ void _bli_array_wrap(void *arr_v, uint arr_len, size_t arr_stride, int dir)
     memcpy(arr, buf, arr_stride);
   }
   else {
-    BLI_assert(0);
+    BLI_assert_unreachable();
   }
 }