Allow to disable default resolver

[bertho-zero]

By default eslint merges the config, making it impossible to use a custom resolver with option without the default resolver node being added.

Try 1

settings: {
  'import/resolver': {
    [path.resolve(__dirname, './resolver')]: { /* some options */ },
  },
},

Then the following resolvers are used:

{
  '/home/.../eslint-config/resolver': {},
  node: { extensions: [ '.js', '.jsx', '.json' ] }
}

Try 2:

settings: {
  'import/resolver': {
    [path.resolve(__dirname, './resolver')]: { /* some options */ },
    node: false,
  },
},

Then the following resolvers are used:

{
  '/home/.../eslint-config/resolver': {},
  node: false,
}

And the node resolver is still used, same with null, undefined or other

Try 3:

I can only disable resolver node by doing this, but I can't pass any options:

settings: {
  'import/resolver': path.resolve(__dirname, './resolver'),
},

---

I propose as a solution not to use a resolver if its configuration is equal to false.