[WIP] Add Game Settings API contracts to Plugin Exports

[Cryotechnic]

This pull request introduces a new declarative game settings contract to the plugin core library (v0.1.6.0), enabling plugins to describe, serialize, and manage game settings pages in a standardized way. The main features include new data structures for settings pages, launcher and plugin-side APIs for settings access and mutation, and related test coverage. The library version is incremented to reflect these additions.

Game Settings Contract Implementation

• Added new types for declarative game settings: GameSettingsPage, GameSettingsSection, GameSettingEntry, GameSettingChoice, and GameSettingKind, enabling plugins to define settings pages with various entry types (toggle, text, number, slider, choice). (UI/Settings/GameSettingsPage.cs [1] UI/Settings/GameSettingsSection.cs [2] UI/Settings/GameSettingEntry.cs [3] UI/Settings/GameSettingChoice.cs [4] UI/Settings/GameSettingKind.cs [5]
• Implemented serialization and deserialization for the settings page contract using source-generated JSON context for efficient ABI transfer. (UI/Settings/GameSettingsPageSerializer.cs UI/Settings/GameSettingsPageSerializer.csR1-R20)

Plugin Core and Launcher Integration

• Added new plugin ABI exports for getting the settings page, setting a value, and applying settings, with safe marshalling and error handling. (SharedStatic.V1Ext_Update6.cs [1] SharedStatic.V1Ext.cs [2]
• Provided a launcher-side utility GameSettingsExtension.GameSettingsContext to access these APIs, check feature availability, and manipulate settings from the launcher. (Utility/GameSettingsExtension.cs Utility/GameSettingsExtension.csR1-R115)

Versioning and Documentation

• Bumped the core library version to v0.1.6.0 and updated the implementation standard in the documentation to reflect the new version and features. (SharedStatic.cs [1] README.md [2]

Testing and CLI Enhancements

• Added a test for the game settings contract round-trip and a corresponding CLI entry point for manual verification. (PluginTest/Test.GameSettings.cs [1] PluginTest/Program.cs [2] [3]

These changes establish a robust, extensible foundation for plugin-defined settings pages, facilitating future UI and integration work.