LibJS: Can not parse dates without leading zero

[dotnetCarpenter]

Build fe8a64d can not parse dates, where the month is without a leading zero - unless there is a time part.

Using /Build/lagom/bin/js :

> new Date ("2024-7-24")
[Date] Invalid Date
> new Date ("2024-7-24 10:00")
[Date] Wed Jul 24 2024 10:00:00 GMT+0200 (Central European Summer Time)
> new Date ("2024-07-24")
[Date] Wed Jul 24 2024 02:00:00 GMT+0200 (Central European Summer Time)

Using V8:

> new Date ("2024-7-24")
2024-07-23T22:00:00.000Z // <- probably not what you want
> new Date ("2024-7-24 10:00")
2024-07-24T08:00:00.000Z
> new Date ("2024-07-24")
2024-07-24T00:00:00.000Z

Using SpiderMonkey:

> new Date ("2024-7-24")
Date Wed Jul 24 2024 02:00:00 GMT+0200 (Central European Summer Time)
> new Date ("2024-7-24 10:00")
Date Wed Jul 24 2024 10:00:00 GMT+0200 (Central European Summer Time)
> new Date ("2024-07-24")
Date Wed Jul 24 2024 02:00:00 GMT+0200 (Central European Summer Time)

Since YYYY-M-DD is not a valid ISO 8601 date, the behaviour is probably undefined in any spec but I've seen it in the wild.

With Ladybird's sister project, also named Ladybird, I saw yesterday on youtube.com, the following error log:

10309.331 WebContent(23165): Unable to parse date string: "2024-7-24"

Log from Ladybird yesterday (2024-09-13)

Today I checked with Serenity's Ladybird and did not see the same error. But I assume the date is dynamic on youtube.com.

Related: #19030 LadybirdBrowser/ladybird#1395