Parse week and year

**Describe the bug**
We have a need to calculate week numbers backwards from a given week year, for example:

`week: 02, year: 2022` ->` [{week: 01, year: 2022}, {week: 53, year: 2022}]`

In order to do this, we are creating a dayjs object like this:

`dayjs().weekYear(year).week(week)` and then subtracting 1 week at a time.

However, we have found that doing it like this is prone to developer errors, as doing something like this:

`dayjs().week(week).weekYear(year)`

returns an incorrect date in some cases.

Therefore, we want to create the dayjs object already parsed in the correct moment in time, as shown in the [docs](https://day.js.org/docs/en/parse/string-format) for example.

However, this feature is unavailable if we want to set by year and week **only**.

**Expected behavior**

`dayjs('2022-53', 'YYYY-WW').format()`

returns

`2022-12-25`

``

**Information**
- Day.js Version [e.g. v1.11.2]
- OS: osx Monterey 12.5.1
- Browser Chrome 109.0.5414.87
- Time zone: [e.g. GMT+02:00 (Asia/Jerusalem)]

Start with the string-format parsing behavior described in the linked Day.js documentation and reproduce dayjs('2022-53', 'YYYY-WW'). Check how week and week-year values are currently parsed and tested. Done means the year-week input resolves to the expected date without depending on the order of weekYear() and week().

Written by the indexing model from the issue text.