planner: support foreign key choose parent schema as default in CreateTable stmt (#12548)

[3pointer]

cherry-pick #12548 to release-2.1

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What problem does this PR solve?

Aligned with MySQL behavior

drop database if exists fk_test;
create database if not exists fk_test;
create table fk_test.t1 (c1 int not null primary key);
create table fk_test.t2 (id int not null primary key, c1 int not null, constraint foreign key (c1) references t1(c1));

MySQL can deal with above sql well, but TiDB will get ERROR 1046 (3D000) at line 4: No database selected

What is changed and how it works?

if foreign key has no schema, use parent table schema

Check List

Tests

• Unit test

Code changes

• NA

Side effects

• NA

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix a compatibility issue that if the foreign key constraint in CREATE TABLE statement has no schema, schema of the created table should be used instead of returning No Database selected error.

[crazycs520]

LGTM

[crazycs520]

/run-all-tests

[bb7133]

LGTM

[sre-bot]

Sorry @bb7133, you don't have permission to trigger auto merge event on this branch.