Add DEFAULT support for CURRENT_DATE, CURRENT_TIME, LOCALTIME, LOCALTIMESTAMP

[dereuromark]

Summary

• Expand automatic SQL function handling to support more standard SQL datetime defaults without requiring Literal::from()
• Add CURRENT_DATE support for date columns
• Add CURRENT_TIME and LOCALTIME support for time columns
• Add LOCALTIMESTAMP support for datetime/timestamp columns
• Update documentation with new column type options

Details

SQL Function	Valid Column Types
CURRENT_TIMESTAMP	datetime, timestamp, time, date
CURRENT_DATE	date
CURRENT_TIME	time

Dropped (not supported yet also in ORM):

SQL Function	Valid Column Types
LOCALTIMESTAMP	datetime, timestamp
LOCALTIME	time

Each function is only left unquoted when used with appropriate column types. Using them with incompatible types (e.g., CURRENT_DATE on a string column) will quote the value as a literal string.

Usage

// Now works without Literal::from()
$table->addColumn('birth_date', 'date', ['default' => 'CURRENT_DATE']);
$table->addColumn('start_time', 'time', ['default' => 'CURRENT_TIME']);

//Dropped again
//$table->addColumn('created_at', 'datetime', ['default' => 'LOCALTIMESTAMP']);

[dereuromark]

I am also fine not supporting LOCALTIMESTAMP/LOCALTIME in favor of the other 3, if we want to keep it simpler.

[markstory]

I am also fine not supporting LOCALTIMESTAMP/LOCALTIME in favor of the other 3, if we want to keep it simpler.

I don't think we have support for LOCALTIME/LOCALTIMESTAMP in the reflection APIs. That will make snapshots lossy.

[dereuromark]

I guess you are also not interested in supporting them correct? Otherwise we could fix up core support first here.

[markstory]

I guess you are also not interested in supporting them correct? Otherwise we could fix up core support first here.

We've never had anyone ask for support for them. We can always add support in the future when folks need it.

[dereuromark]

if no one asked for it yet, maybe we dont need to widen the scope now.
I will remove those then, and simplify this PR.