planner: prevent the optimizer from using different versions of stats of a table during optimization

[qw4990]

Enhancement

create table t (a int, b int, key(a), key(b));
insert into t values (1, 1);
analyze table t;  -- stats-ver1
set global tidb_stats_load_sync_wait=1;

-- restart TiDB
explain select * from t where a=1; -- load stats-col-a

explain select * from t where a=1 and b=1; -- load stats-col-b timeout
+-------------------------+---------+-----------+---------------+-----------------------------------------------+
| id                      | estRows | task      | access object | operator info                                 |
+-------------------------+---------+-----------+---------------+-----------------------------------------------+
| TableReader_7           | 2.00    | root      |               | data:Selection_6                              |
| └─Selection_6           | 2.00    | cop[tikv] |               | eq(test.t.a, 1), eq(test.t.b, 1)              |
|   └─TableFullScan_5     | 2.00    | cop[tikv] | table:t       | keep order:false, stats:partial[b:allEvicted] |
+-------------------------+---------+-----------+---------------+-----------------------------------------------+

In the second query, the optimizer uses 2 versions of statistics of table t where stats-col-a is loaded and then stats-ver1 is used while stats-col-b is not loaded and then pseudo is used, which seems risky.
Should we force the optimizer to always use one statistics version of a table during optimization? (all stats-ver1 or all stats-pseudo, no in-between state, not use them together).