sql_mode ALLOW_INVALID_DATES is not supported

[morgo]

Feature Request

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

Relates to #2738 - currently ALLOW_INVALID_DATES is not supported. It is not commonly used, but could be useful for compatibility.

Describe the feature you'd like:

# testcase
CREATE TABLE d1 (d DATE);
SET sql_mode='STRICT_TRANS_TABLES,ALLOW_INVALID_DATES';
INSERT INTO d1 VALUES ('2010-00-01');

Passes in MySQL, produces this in TiDB:

MySQL [test]> SET sql_mode='STRICT_TRANS_TABLES,ALLOW_INVALID_DATES';
ERROR 1105 (HY000): ERROR 1231 (42000): Variable 'sql_mode' can't be set to the value of 'ALLOW_INVALID_DATES'
MySQL [test]> INSERT INTO d1 VALUES ('2010-00-01');
ERROR 1292 (22007): Incorrect datetime value: '2010-00-01'

Describe alternatives you've considered:
Possible to document as unsupported.

Teachability, Documentation, Adoption, Migration Strategy:
Improves compatibility with MySQL.