Support for more datetime SQL functions

there are many ANSI SQL standard date time functions that we should support
`DateTimeFunction` already support many of these implementations but the semantics are different thus it is good to support the standardized ANSI function format:
- `{fn YEAR(date)}`, `{fn MONTH(date)}`, ...
- `DATE(string)`, Equivalent to `CAST(string AS DATE)`
- `{fn NOW()}`
- `TIMESTAMPADD(timeUnit, integer, datetime)`
- `TIMESTAMPDIFF(timeUnit, datetime, datetime2)`
- `TO_DATE(string, format)`
- `TO_TIMESTAMP(string, format)`
- `INTERVAL timeWithUnit [ TO timeWithUnit ]`

we might also consider supporting some other non SQL standard such as:
- `DATE_ADD(, )` or `DATEADD` in mysql/presto/sqlserver
- `TO_UNIXTIME` / `FROM_UNIXTIME`

Start by reading the existing DateTimeFunction implementation mentioned in the issue and compare its semantics with the listed ANSI SQL forms. Define the supported function scope and verify that the standardized forms, including DATE, NOW, TIMESTAMPADD, TIMESTAMPDIFF, TO_DATE, TO_TIMESTAMP, and INTERVAL, behave as specified.

Written by the indexing model from the issue text.