Ignore plugin: allow for finegrained ignoring of specific AST nodes (without their children)

[nicojs]

Is your feature request related to a problem? Please describe.

The current ignore plugin specification allows you to ignore specific AST nodes. It also includes ignoring all descendants of that node. This is elegant when you want to ignore logger.log(...) for example, but not for the use case of the Angular Ignorer.

In this example, we would actually only want to ignore the mutant on line 9 and the mutant on line 10, but because mutants on line 11-19 are on nodes which are descendants the node on line 9, we automatically also ignore all of them.

Describe the solution you'd like
I think returning a string from shouldIgnore can keep working as it is, but we should also allow to return an object with a 'mode'.

interface IgnoreDescription {
  message: string;
  mode: 'descendants' | 'self';
}

interface Ignorer {
  shouldIgnore(path: NodePath): string | undefined | IgnoreDescription;
}

Describe alternatives you've considered
I don't think there are other solutions. Leaving descendant nodes unmutated is not ellegant.