feat(ios): add feature state api

[MarkusWendorf]

Implements feature state for iOS. feature-state was already implemented in the core.

This is an alternative implementation to #3858, deliberately aligned with the API shape that shipped for Android in #4219.

I also added a vector-tile example to Android, so that we now have a GeoJSON example AND a vector-tile example for feature-state on both iOS and Android.

Tests added:

• platform/ios/test/MLNFeatureStateTests.swift —
  MLNFeatureStateTests.testFeatureStateRoundTrip (integration test through the Swift source
  API).
• test/api/query.test.cpp — Query.QuerySourceFeatureStates and
  Query.RemoveSourceFeatureState (set/get round-trip and key-/feature-level removal via the
  renderer).
• test/map/map.test.cpp — Map.FeatureStateChangesRenderedStyle, an end-to-end test asserting
  that a feature-state change actually alters rendered pixel output through a data-driven
  ["case", ["boolean", ["feature-state", "active"], …]] fill-color expression.

Co-authored with AI: Anthropic Fable/Opus 4.8

[louwers]

Thanks Markus. I think an implementation that aligns with Android makes more sense.

Will have a look at this tomorrow.

[MarkusWendorf]

@louwers not sure if I jumped the shark here but I assumed your PR is out-dated now that the source centric API from Android was merged.

[github-actions]

Bloaty Results 🐋

Compared to main

    FILE SIZE        VM SIZE    
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  [ = ]       0  [ = ]       0    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-4420-compared-to-main.txt

Compared to d387090 (legacy)

    FILE SIZE        VM SIZE    
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   +54% +62.9Mi  +471% +28.1Mi    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-4420-compared-to-legacy.txt

[github-actions]

Benchmark Results ⚡

Benchmark                                                          Time             CPU      Time Old      Time New       CPU Old       CPU New
-----------------------------------------------------------------------------------------------------------------------------------------------
OVERALL_GEOMEAN                                                 +0.0066         +0.0066             0             0             0             0

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/benchmark-results/pr-4420-compared-to-main.txt

[github-actions]

Bloaty Results (iOS) 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0% +4.30Ki  [ = ]       0    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results-ios/pr-4420-compared-to-main.txt