[google_maps_flutter] Migrate iOS heatmaps to Pigeon

[stuartmorgan-g]

Replaces the legacy JSON serialization of heatmaps with fully typed Pigeon data.

Updates the min Flutter SDK version to 3.35 (stable N-1) because there's an analysis difference between 3.32 and 3.35 in some of the new Dart code, and it's easier to just drop 3.32 now than to add a suppression and then clean it up later.

Final iOS portion of flutter/flutter#117907

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩↩²↩³

[gemini-code-assist]

Code Review

This pull request is a great improvement, migrating the iOS heatmap implementation from legacy JSON serialization to a fully typed Pigeon data model. This refactoring significantly enhances type safety, code clarity, and maintainability. The changes are comprehensive, covering Dart and Objective-C code, updating tests to reflect the new data structures, and correctly removing the old serialization logic. I have one minor suggestion for a small efficiency improvement in the Dart code.

[gemini-code-assist]

To avoid iterating over gradient.colors twice, you can use a single loop to build both the colors and startPoints lists. This can be slightly more efficient and arguably makes it clearer that the two lists are built in tandem.

staticPlatformHeatmapGradient?_platformHeatmapGradientFromHeatmapGradient(
HeatmapGradient? gradient,
) {
if (gradient ==null) {
returnnull;
}
finalList<PlatformColor> colors =<PlatformColor>[];
finalList<double> startPoints =<double>[];
for (finalHeatmapGradientColor c in gradient.colors) {
colors.add(PlatformColor(
red: c.color.r,
green: c.color.g,
blue: c.color.b,
alpha: c.color.a,
));
startPoints.add(c.startPoint);
}
returnPlatformHeatmapGradient(
colors: colors,
startPoints: startPoints,
colorMapSize: gradient.colorMapSize,
);
}