sqlparser errors on altering a table's charset

[jmhodges]

Parsing schema statements like

alter table users CHARSET=utf8mb4;

causes sqlparser to return errors like:

syntax error at position 26 near 'charset'

when passed to NewStringTokenizer and then ParseNextStrictDDL.

That statement is a valid syntax for mysql. It sets the table's default charset to utf8mb4;

[jmhodges]

Closing this in favor of #5705