SwiftUI RouteProgress support

Nobody has claimed this yet.

## New Feature

I am building a custom navigation UI and have been able to accomplish this pretty nicely using SwiftUI. However there just is no smooth way to handle RouteProgress updates.

This is currently how I'm handling showing the route and the progress but it is nowhere near as smooth as the drop-in NavigationViewController. The line annotation doesn't stay aligned with the Puck and is mostly updating too early and ahead or behind and too late.

# Extracting remaining route coordinates
`private func updateRouteLines(with routeProgress: RouteProgress) {
var coordinates = routeProgress.currentLegProgress.currentStepProgress.remainingStepCoordinates()

for step in routeProgress.currentLegProgress.remainingSteps {
if let stepCoordinates = step.shape?.coordinates {
coordinates.append(contentsOf: stepCoordinates)
}
}

// Get coordinates for all remaining legs
for leg in routeProgress.remainingLegs {
for step in leg.steps {
if let stepCoordinates = step.shape?.coordinates {
coordinates.append(contentsOf: stepCoordinates)
}
}
}

remainingStepRouteCoordinates = coordinates
}`

# Annotation
`PolylineAnnotationGroup {
PolylineAnnotation(lineCoordinates: remainingStepRouteCoordinates)
.lineColor(.init(UIColor.white))
.lineWidth(8)
}
.lineCap(.round)
.slot(.middle)
`

## Why
I can't use the NavigationViewController due to custom UI/UX requirements. This would unlock SwiftUI navigation capabilities for Mapbox developers looking to use SwiftUI.

Start by reviewing the SwiftUI RouteProgress flow described in the issue, including remainingStepCoordinates(), remainingLegs, and the PolylineAnnotationGroup/PolylineAnnotation usage. Compare this with the drop-in NavigationViewController behavior; done means SwiftUI users can receive smooth RouteProgress updates while the route line stays aligned with the Puck.

Written by the indexing model from the issue text.