[no-unused-vars] False positive with parameter decorators

[raymondfeng]

Repro

{
  "rules": {
    "@typescript-eslint/no-unused-vars": [
      "error",
      {
        "vars": "all",
        "args": "none"
      }
    ]
  }
}

// Create a parameter decorator
const log = function(target: Object, method: string, index: number) {
  console.log('decorating %s[%d]', method, index); 
}

class MyService {
  constructor(@log public x: string) {}
}

Expected Result

No violation of unused-vars is reported.

Actual Result

It complains that log is declared but not used.

Additional Info

Versions

package	version
@typescript-eslint/eslint-plugin	1.4.2
@typescript-eslint/parser	1.4.2
TypeScript	3.4.5
ESLint	5.16.0
node	12.1.0
npm	6.9.0