Use unique ID as rawvalue for dropdown, instead of display value

[Copilot]

Dropdowns, checkbox lists, and radio button lists previously used display values as raw values, causing issues when multiple options share the same display text or when display values change.

Changes

• New mapping infrastructure: Added RawValueMapping<T> and OneToOneMapping<Ta, Tb> to maintain bidirectional mappings between GUID-based raw values and display values
• Updated widget implementations: Modified DropDown, CheckBoxList, RadioButtonList and their generic counterparts to generate unique GUIDs for each option instead of using display values directly
• Enhanced debugging: Added logging in LoadResult to track raw value to display value resolution

Example

var dropdown = new DropDown(new[] { "Option A", "Option A", "Option B" });
// Previously: Raw values were "Option A", "Option A", "Option B" - ambiguous
// Now: Raw values are unique GUIDs, display values remain as shown

This ensures stable value tracking even when display text duplicates or changes.

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