Support RegExp in `ignore` option of `no-unresolved`

_An array of `RegExp` pattern strings_ must be set to the [`ignore`](https://github.com/import-js/eslint-plugin-import/blob/v2.31.0/docs/rules/no-unresolved.md#ignore) option of the `import/no-unresolved` rule. With a string, linters (and text editors) don't know that it contains a regex and can't check it.

It would be simpler and safer if we could set the `RegExp` directly:

```javascript
export default [{
rules: {
"import/no-unresolved": ["error", { ignore: [/\.img$/v] }],
}
]};

Start with the no-unresolved rule and the linked documentation for its ignore option. Locate how ignore values are currently handled and where this rule is tested; done means direct RegExp values are accepted for ignore and the existing ignore behavior remains covered.

Written by the indexing model from the issue text.