DatePicker: Fix day's labels for shifting by 1 in specific usr and website timezone combination

[MaksVeter]

What?

Fixes the days labels become wrong after the DST time when user is in UK and Website has US Timezone.

Why?

#67480

How?

Add 15 hours to day before pathing it to Day component to avoid the DST impact described in a bug (in the similar maner as date-fns lib do)

Testing Instructions

1. Set local UK timezone
2. Set website US timezone (America/New_York)
3. Go to post with Gutenberg enabled
4. Open the post date picker
5. find the October 2024 and November 2024
6. Check the day's labels

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

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