New snippet "set-constant"
I suggest adding a new snippet "set-constant". In many cases, it can be very useful. In uBlock Origin, this is implemented as follows: https://github.com/gorhill/uBlock/wiki/Resources-Library#set-constantjs-
More details: https://github.com/gorhill/uBlock/blob/a94df7f3b27080ae2dcb3b914ace39c0c294d2f6/assets/resources/scriptlets.js#L394