Support Time.new with string timestamp argument and error when invalid

[rwstauner]

closes #3693

Use a regexp to quickly detect if a timestamp string is valid.
If it isn't raise an ArgumentError for consistency with CRuby 3.2+.

I added a few new specs for behavior I noticed that I didn't see in the existing specs.
It's not that difficult to match the existing error messages, but I'm not sure how valuable they are.

Here are some examples of the differences:

Expected ArgumentError (missing sec part: 00:56 )
but got: ArgumentError (can't parse: "2020-12-25 00:56 +09:00")

Expected ArgumentError (subsecond expected after dot: 00:56:17. )
but got: ArgumentError (can't parse: "2020-12-25 00:56:17. +0900")

Expected ArgumentError (year must be 4 or more digits: 021)
but got: ArgumentError (can't parse: "021-12-25 00:00:00.123456 +09:00")

Expected ArgumentError (mon out of range)
but got: ArgumentError (can't parse: "2020-13-25 00:56:17 +09:00")

As discussed, this relaxes the error message specs to keep the code simple.

This removes the "fails" tags for the "Time.new with a String argument" specs except for the three precision related ones which TruffleRuby isn't doing anything with yet.

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[eregon]

Thank you, it look great and simple.
I left some comments to improve it further.

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[eregon]

Beautiful :)