btr_index_rec_validate_report(), btr_index_rec_validate(): Add const
qualifiers to page, rec, index.

row_vers_old_has_index_entry(), row_vers_build_for_consistent_read():
Add const qualifier to rec.

row_vers_build_for_semi_consistent_read(): Add const qualifier to rec
and old_vers.

row_sel_store_row_id_to_prebuilt(): Add const qualifiers to
index_rec, index, offsets.

row_sel_build_prev_vers_for_mysql(): Add const qualifier to rec.

row_sel_get_clust_rec_for_mysql(): Add const qualifier to rec and out_rec.

row_sel_try_search_shortcut_for_mysql(): Add const qualifier to out_rec.