Fills a text field or textarea, after clearing its value, with the given string.
Field is located by name, label, CSS, or XPath.

```js
// by label
I.fillField('Email', 'hello@world.com');
// by name
I.fillField('password', secret('123456'));
// by CSS
I.fillField('form#login input[name=username]', 'John');
// or by strict locator
I.fillField({css: 'form#login input[name=username]'}, 'John');
```
@param {CodeceptJS.LocatorOrString} field located by label|name|CSS|XPath|strict locator.
@param {string} value text value to fill.