Regression in 4.3.1: this.directions.setDestination and this.directions.setOrigin no longer populate sources.directions

Nobody has claimed this yet.

In version 4.2.0, calling the following:

```javascript
this.directions.setDestination(this.destinationLocation);
this.directions.setOrigin([e.coords.longitude, e.coords.latitude]);

console.log(this.directions);
console.log(this.map.getStyle().sources.directions.data);
```

Correctly populates `sources.directions` with two features.

However, after upgrading to 4.3.1, this behavior has changed. The same calls no longer populate `sources.directions` as expected.

### Expected Behavior:
- After setting the destination and origin, the `sources.directions` should contain two features.

### Actual Behavior:
- In 4.3.1, `sources.directions` remains empty or does not populate as it did in 4.2.0.

### Steps to Reproduce:
1. Initialize directions and map in 4.3.1.
2. Set destination using `this.directions.setDestination`.
3. Set origin using `this.directions.setOrigin`.
4. Check the contents of `sources.directions` using `console.log(this.map.getStyle().sources.directions.data)`.

### Workaround:
Provide any workaround you've found, or indicate none if not available.

### Environment:
- Version: 4.3.1
- Browser/Device: [Add details]

Could you investigate the change between versions and provide guidance on the correct way to populate `sources.directions` in 4.3.1?

Compare the 4.2.0 and 4.3.1 implementations around directions.setDestination and directions.setOrigin, then inspect the map.getStyle().sources.directions.data result in a minimal reproduction. Done means identifying the regression or changed contract and documenting the correct way to obtain or populate the two expected features in 4.3.1.

Written by the indexing model from the issue text.