Improve 'set-cookie' and 'set-cookie-reload' — add 'declined' to predefined constants

[mu-hun]

The set-cookie scriptlets currently allow only predefined constants or numeric values.

Some websites use declined as the consent cookie value, which cannot currently be set.

Example: https://www.tempemail.cc. I discovered it while working on AdguardTeam/AdguardFilters#226132.

After clicking "Decline", the site sets:

gdpr-consent=declined

Attempting to reproduce this rule does not work:

www.tempemail.cc#%#//scriptlet('set-cookie', 'gdpr-consent', 'declined')

However, denied works because it is in the allowed constant list:

www.tempemail.cc#%#//scriptlet('set-cookie', 'gdpr-consent', 'denied')

Proposal:
Add declined to the predefined constants accepted by:

• set-cookie
• set-cookie-reload

[krystian3w]

In theory, it’s worth synchronising again with uBlock: https://github.com/gorhill/uBlock/blob/ab8baaf833911fb3acb320d0a5b903e1690ed087/src/js/resources/cookie.js#L28-L51

That said, the pool has been pretty much exhausted on uBO: gorhill/uBlock#3936 (there haven't been any reviews from gorhill or anyone from uAssets in the last six months) (Then AdGuard will start to force uBO to change its mind or there will be a rift on uBo's side).