Fixing heatmap example

[AndrewSepic]

Changes in this PR

This PR fixes errors in the HeatmapLayerGlobeExample.swift file which was causing the circle Layer to not render on the map. This was discovered when I was working on creating an example description for this example in this PR and realized that the createCircleLayer() was failing to render.

The error had 2 causes

1. createCircleLayer() declares the Earthquakes source after it is already declared above
2. The interpolate function requires literal numeric values and this was using expressions.
3. Interpolate requires numeric literals in strictly ascending order and this example included 2 steps with the value of 1.

All of the above errors are fixed in this PR.

Pull request checklist:

• Describe the changes in this PR, especially public API changes.
• Include before/after visuals or gifs if this PR includes visual changes.

Before	After

Video with transition of layers

Screen.Recording.2024-12-03.at.10.52.40.AM.mov

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