Recurrence and Exclude dates are converted incorrectly for locations east of UTC

[sdetweil]

the code parses the RECURRENCE-ID and EXDATE strings into date() objects.

then extracts the date string to use as the lookup key..

except it uses toISOString()

curr.recurrenceid.toISOString().slice(0, 10)

toISOString uses UTC offset 0.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString#:~:text=Syntax-,Date.prototype.toISOString(),denoted%20by%20the%20suffix%20Z%20.
(see the 'Z' at the end)

which for the person in Germany is yesterday . oops...

EXDATE;VALUE=DATE:20221123
RECURRENCE-ID;VALUE=DATE:20221123

as no time is specified, these are local time..

i created another function to return the local time date.

[sdetweil]

fixed by #345