Cannot find interface declaration for 'ChartXAxisRenderer' when subclassing XAxisRenderer

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## What did you do?

I have added Charts to an iOS swift project with SPM. I am able to create charts without any issues. I want to subclass the XAxisRenderer class to customise the limit line label like shown below.

```
class CustomRenderer: XAxisRenderer {
override func renderLimitLineLabel(context: CGContext, limitLine: ChartLimitLine, position: CGPoint, yOffset: CGFloat) {
// My changes
ChartUtils.drawText(
context: context,
text: label,
point: point,
align: align,
attributes: attributes
)
}
}

```

So that I can then apply it to my LineChart like:
```
self.lineChart.xAxisRenderer = CustomRenderer(
viewPortHandler: self.lineChart.viewPortHandler,
xAxis: self.lineChart.xAxis,
transformer: self.lineChart.getTransformer(forAxis: .left)
)
```

## What did you expect to happen?

I can subclass the XAxisRenderer and pass it to my chart. I do have a bridging header file because I have some objective-c view controllers in the swift project. I have also marked "Always Embed Swift Standard Libraries" under build options. I researched and didn't see any issues like the one I am facing. I have a feeling it's something I missed but I am unable to find the cause.

## What happened instead?

However subclassing causes the build to fail with the following error...

## Charts Environment

**Charts version/Branch/Commit Number:** 3.5.0
**Xcode version:** Version 11.5 (11E608c)
**Swift version:** 5
**Platform(s) running Charts:** iOS
**macOS version running Xcode:** -