Add the missing `SQLDatabase.alter(table: any SQLExpression)` method

Each of the various query builders have overloads on `SQLDatabase` which accept `any SQLExpression` parameters, except for `SQLAlterTableQueryBuilder`. The missing `SQLDatabase.alter(table: any SQLExpression)` overload is now provided. Additional changes: - Fixed several minor issues in the API docs. - The minimum required Swift version is now 5.10.