`NcDateTimePicker` week labels off by one

[raimund-schluessler]

Originally reported in nextcloud/tasks#2366.

See here:

The first week of January should be the week with the starting year's first Thursday in it (the formal
ISO definition), see https://en.wikipedia.org/wiki/ISO_8601

In the screenshot above, the first week starts 7 days to early. What is labeled as 1 should be 53 of 2022.

[raimund-schluessler]

There seems to be a solution using moment.js

mengxiong10/vue2-datepicker#679 (comment)

[susnux]

It can be fixed without moment -> no need for "dead" software 😉