unused-fields: fake positive on different scopes

[caiotoon]

The rule is currently matching any occurrences in the entire file, even when usage is in different functions. The following invalid test fails:

    {
      code: `
        function method1() {
          graphql\`fragment Test2 on SomeEntity {
            unused1
          }\`;
          const { unused1 } = node;
          return unused1;
        }
        function method2() {
          graphql\`fragment Test on Page {
            unused1
            used1
          }\`;
          var { used1 } = node;
        }
      `,
      errors: [
        {
          message: unusedFieldsWarning('unused1'),
          line: 7
        }
      ]
    }

The message is currently clear and matches the behaviour, so I believe this might have been intentional given the difficulty of trying to maintain scope and context for the validation.

[...] this file does not seem to use it directly. [...]

Opening this one to track the possibility of adding a new rule to validate considering the scope.