bug(tsql): fix datepart handling when part is quoted

[flow3d]

Previous discussion here
Summary - while this doesn't seem valid, this is a legitimate TSQL syntax (escaping date parts).
It's already supported in dateadd & datediff, but was missing from datepart.

Validated here as well with select datepart("dd",'2025-12-13') on SQL Server 2022

-- more details
trust me, I don't like this being a valid syntax neither, but it is :)

select @reportdate = datepart("dd",getdate())

the above is a valid TSQL syntax.
Also - note that you guys already support this syntax in other date functions:

select dateadd("dd", -DAY(getdate()), DATEADD("mm", 0, detdate()))

is parsed into:

[Select(
   expressions=[
     DateAdd(
       this=DateAdd(
         this=Anonymous(this=detdate),
         expression=Literal(this=0, is_string=False),
         unit=Var(this=MONTH)),
       expression=Neg(
         this=Day(
           this=CurrentTimestamp())),
       unit=Var(this=DAY))])]