Fixes #5259. AOT: use source-generated JSON serializer for dictionary construction in DeepCloner

[Copilot]

Fixes

DeepCloner.CreateDictionaryInstance uses Activator.CreateInstance(dictType) to construct cloned dictionaries. AOT trimming removes default constructors of closed generic Dictionary<,> types not statically reachable, causing MissingMethodException at module-init time. The previous fix (#5240) added a typed clone path for one dictionary; this is whack-a-mole — any new config dictionary type triggers the same crash.

Proposed Changes/Todos

• CreateDictionaryInstance now tries SourceGenerationContext (source-generated JSON serializer) to create empty dictionary instances before falling back to Activator.CreateInstance. All config dictionary types are already registered there, so this fixes the category.
• Removed CloneHardCodedPropertyValue and its per-type helpers (CloneKeyBindings, ClonePlatformKeyBinding, CloneKeyArray) from ConfigurationManager — DeepCloner.DeepClone handles all dictionary types generically now.
• Added test for Dictionary<ColorName16, string> cloning (the specific crash from this issue).

Key change in CreateDictionaryInstance:

// Before falling back to Activator.CreateInstance:
JsonTypeInfo? jsonTypeInfo = ConfigurationManager.SerializerContext.GetTypeInfo (dictType);
if (jsonTypeInfo is not null)
{
    IDictionary? result = JsonSerializer.Deserialize ("{}", jsonTypeInfo) as IDictionary;
    if (result is not null) { return result; }
}

Typed paths remain for ConcurrentDictionary<string, ThemeScope> and Dictionary<string, Scheme?> which require custom comparers.

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[tig]

@BDisp you'll dig the updates nativeaot example i think. ;-)

[tig]

See #4367 (comment)