Function getWagtailDirectives

getWagtailDirectives(): string
Extract the Wagtail directives from the URL fragment.

This follows the algorithm described in https://wicg.github.io/scroll-to-text-fragment/#extracting-the-fragment-directive for extracting the fragment directive from the URL fragment, with a few differences:
- We use a :w: delimiter instead of the proposed :~: delimiter.
- We don't remove our directive from the URL fragment.
Returns string
a string of Wagtail directives, if any, in the style of URL search parameters.
Example
```
window.location.hash = '#:w:contentpath=abc1.d2e.3f'
// getWagtailDirectives() === 'contentpath=abc1.d2e.3f'
```
Example
```
window.location.hash = '#an-anchor:w:contentpath=abc1.d2e.3f'
// getWagtailDirectives() === 'contentpath=abc1.d2e.3f'
```
Example
```
window.location.hash = '#hello:w:contentpath=abc1.d2e.3f&unknown=123&unknown=456'
// getWagtailDirectives() === 'contentpath=abc1.d2e.3f&unknown=123&unknown=456'
```
- Defined in utils/contentPath.ts:25