[google_maps_flutter] Convert heatmap controller to Swift

[stuartmorgan-g]

This converts HeatmapController and the remaining utility functions to Swift in the _sdk* packages.

The final remaining Obj-C code will be migrated in a follow-up PRs.

The conversion process was:

• Initial conversion via Gemini, with explicit instruction to keep the structure the same.
• Side-by-side manual review of the old and new versions of the files.
• Manual fixes and improvements.

The conversion code utils have much more change than previous PRs, since the direct conversion code felt very non-idiomatic in Swift. Almost all of the free functions for Pigeon<->Maps SDK type conversions were converted to extensions on the Pigeon types:

• To avoid the fragile pattern of putting extension methods on types we don't control (which can lead to collisions), all the extensions are on the Pigeon types, and so the APIs aren't symmetrical:
  • Maps -> Pigeon is done via a convenience constructor (generally called make(from:)
  • Pigeon -> Maps is done via a toMapsSDKClassName() method on the Pigeon type (I'm not sold on that naming pattern; alternate suggestions welcome)
• Conversions functions that were array-based have been changed to single-element conversions following the pattern above, and then the call sites changed to just map that conversion function, since map is a simple and idiomatic pattern in Swift, unlike the loop-and-add construction that had been required in Obj-C.
  • This in turn caused some tests to be simplified, since we didn't need to test things like the number of list items converted, and can instead just test the individual conversion.

The test bridging header is removed since there are no longer any _Test headers.

Part of flutter/flutter#119108

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• 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 followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception 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

[gemini-code-assist]

Code Review

This pull request converts the heatmap controller and data conversion logic from Objective-C to Swift across the iOS packages (sdk9, sdk10, and shared_code), removing several Objective-C files in favor of Swift implementations. The review feedback highlights critical safety issues, pointing out potential runtime crashes from unsafely unwrapping optional values like heatmap.gradient and heatmap.weightedData. Additionally, the reviewer suggests performance optimizations, such as avoiding unnecessary CLLocation heap allocations by passing CLLocationCoordinate2D directly to path-creation helpers, and refactoring redundant image loading logic in ImageUtils.swift.