support push calculation of type 'enum' to TiFlash

Feature Request

Is your feature request related to a problem? Please describe:

1. create table t0 and t1

create table t0(id int primary key, v int, vv enum('A1', 'A2', 'A3'));
create table t1(id int primary key, v int, vv enum('B1', 'B2', 'B3'));

2. execute expain

explain analyze select/*+ read_from_storage(tiflash[a], tiflash[b]) */ a.v, b.v, a.vv, b.vv from t0 a join t1 b on a.id=b.id where a.vv='A1';

there are some warnings:

enum type is used frequently as basic type, so why TiFlash don't support it ?

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

Start by reproducing the two CREATE TABLE statements and the EXPLAIN ANALYZE join query from the issue, then inspect the reported TiFlash warnings. The issue names no source files or tests; done means enum expressions are supported by TiFlash push calculation without those warnings.