Revert "Support setting style JSON on iOS, web"

[gabbopalma]

Reverts #603. This will be merged in release-0.23.0 branch

[Copilot]

Pull Request Overview

This PR reverts a previous change that added support for setting style JSON on iOS and web platforms. The revert is intended for the release-0.23.0 branch to remove this functionality.

Key changes:

• Removes JSON style support from iOS and web platforms
• Reverts web implementation to use style strings instead of style objects
• Updates documentation to clarify JSON styles are only supported on Android

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
maplibre_gl_web/lib/src/ui/map.dart	Reverts setStyle method to not use jsify on style parameter
maplibre_gl_web/lib/src/options_sink.dart	Changes setStyle method back to setStyleString
maplibre_gl_web/lib/src/maplibre_web_gl_platform.dart	Reverts to using styleString and setStyleString method
maplibre_gl_web/lib/src/convert.dart	Removes JSON parsing logic for style strings
maplibre_gl_web/lib/maplibre_gl_web.dart	Removes dart:convert import
maplibre_gl/lib/src/maplibre_map.dart	Updates documentation to specify JSON support is Android-only
maplibre_gl/ios/maplibre_gl/Sources/maplibre_gl/MapLibreMapController.swift	Removes JSON style support and reverts to URL-based styling
maplibre_gl/ios/.gitignore	Removes .build entry
maplibre_gl/README.md	Updates documentation to clarify JSON support limitation

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