[FEATURE]: Generate values based on other columns with $default() and $onUpdate()

### Describe what you want

Currently, `$default($defaultFn)` and `$onUpdate()` don't have access to their adjacent insert/update values.
This would be useful for generating values based on other columns.

Example:
```TypeScript
const userEntity = pgTable('users', {
firstName: varchar('first_name').notNull(),
lastName: varchar('last_name').notNull(),
fullName: varchar('full_name')
.notNull()
.$default((insert) => {
return `${insert.firstName} ${insert.lastName}`;
})
.$onUpdate((update) => {
return `${update.firstName} ${update.lastName}`;
})
});
```

### Search
Access to other columns from `$default()`, `$defaultFn()` `$onUpdate()`
Access to neighbour columns from `$default()`, `$defaultFn()` `$onUpdate()`