Type declaration for GM_* APIs in Violentmonkey.

The APIs should be almost the same as those in Tampermonkey, so @types/tampermonkey should also work.

$ npm i @violentmonkey/types

Add @violentmonkey/types to your tsconfig.json:

{
  "include": [
    "other paths...",
    "node_modules/@violentmonkey/types"
  ]
}