Add DateTime constructor for Base.Libc.Tmstruct

[eulerkochy]

Fixes #31524

[eulerkochy]

Could this be reviewed before feature freeze? Can this be considered as a feature @StefanKarpinski ?

[StefanKarpinski]

This seems sane to me. @quinnj: can you do a quick sanity check and merge if it's good?

[eulerkochy]

@quinnj is it alright now?

[quinnj]

So here's what the docs say for the meaning of TmStruct fields:

Member	Type	Meaning	Range
tm_sec	int	seconds after the minute	0-61*
tm_min	int	minutes after the hour	0-59
tm_hour	int	hours since midnight	0-23
tm_mday	int	day of the month	1-31
tm_mon	int	months since January	0-11
tm_year	int	years since 1900
tm_wday	int	days since Sunday	0-6
tm_yday	int	days since January 1	0-365
tm_isdst	int	Daylight Saving Time flag

So we'll need to adjust the DateTime and Date constructors to account for the TmStruct month being 0-based (0 - 11), and the year being "years since 1900". So if we can make those changes and then add some tests making sure it's all being converted correctly, I think this is looking good.

[eulerkochy]

@quinnj thanks for the type definition, I've corrected the constructor definition, and have added tests.

[eulerkochy]

@StefanKarpinski @quinnj when is the feature freeze?

[StefanKarpinski]

Today. Might get a bit delayed on account of ongoing CI flakiness.

[quinnj]

I think this looks good now!

[eulerkochy]

Bump